From 3bc429487d17081f6c7a4166a171922be0b1c3f4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ho=C3=A0ng?= <93896207+HollandDM@users.noreply.github.com>
Date: Mon, 10 Mar 2025 13:12:36 +0700
Subject: [PATCH] Use process pool for test runner (0.12.x) (#4679)

ported for 0.12.x from #4614

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
---
 .gitignore                                    |   4 +-
 docs/modules/ROOT/pages/javalib/testing.adoc  |   7 +
 .../modules/ROOT/pages/kotlinlib/testing.adoc |   7 +
 docs/modules/ROOT/pages/scalalib/testing.adoc |   8 +
 .../testing/5-test-stealing/build.mill        |  15 +
 .../5-test-stealing/foo/src/foo/Foo.java      |  11 +
 .../foo/test/src/foo/RandomTestsA.java        |  11 +
 .../foo/test/src/foo/RandomTestsB.java        |  10 +
 .../foo/test/src/foo/RandomTestsC.java        |  10 +
 .../foo/test/src/foo/RandomTestsD.java        |  10 +
 .../foo/test/src/foo/RandomTestsE.java        |  10 +
 .../foo/test/src/foo/RandomTestsF.java        |  10 +
 .../foo/test/src/foo/RandomTestsG.java        |  10 +
 .../foo/test/src/foo/RandomTestsH.java        |  10 +
 .../foo/test/src/foo/RandomTestsI.java        |  10 +
 .../foo/test/src/foo/RandomTestsJ.java        |  10 +
 .../foo/test/src/foo/RandomTestsUtils.java    |  11 +
 .../testing/6-test-group-stealing/build.mill  |  19 +
 .../foo/src/foo/Foo.java                      |  11 +
 .../foo/test/src/foo/GroupX1.java             |  10 +
 .../foo/test/src/foo/GroupX10.java            |  10 +
 .../foo/test/src/foo/GroupX2.java             |  10 +
 .../foo/test/src/foo/GroupX3.java             |  10 +
 .../foo/test/src/foo/GroupX4.java             |  10 +
 .../foo/test/src/foo/GroupX5.java             |  10 +
 .../foo/test/src/foo/GroupX6.java             |  10 +
 .../foo/test/src/foo/GroupX7.java             |  10 +
 .../foo/test/src/foo/GroupX8.java             |  10 +
 .../foo/test/src/foo/GroupX9.java             |  10 +
 .../foo/test/src/foo/GroupY1.java             |  10 +
 .../foo/test/src/foo/GroupY10.java            |  10 +
 .../foo/test/src/foo/GroupY2.java             |  10 +
 .../foo/test/src/foo/GroupY3.java             |  10 +
 .../foo/test/src/foo/GroupY4.java             |  10 +
 .../foo/test/src/foo/GroupY5.java             |  10 +
 .../foo/test/src/foo/GroupY6.java             |  10 +
 .../foo/test/src/foo/GroupY7.java             |  10 +
 .../foo/test/src/foo/GroupY8.java             |  10 +
 .../foo/test/src/foo/GroupY9.java             |  10 +
 .../foo/test/src/foo/RandomTestsUtils.java    |  11 +
 .../testing/5-test-stealing/build.mill        |  22 +
 .../5-test-stealing/foo/src/foo/Foo.kt        |  11 +
 .../foo/test/src/foo/RandomTestsA.kt          |  11 +
 .../foo/test/src/foo/RandomTestsB.kt          |  11 +
 .../foo/test/src/foo/RandomTestsC.kt          |  11 +
 .../foo/test/src/foo/RandomTestsD.kt          |  11 +
 .../foo/test/src/foo/RandomTestsE.kt          |  11 +
 .../foo/test/src/foo/RandomTestsF.kt          |  11 +
 .../foo/test/src/foo/RandomTestsG.kt          |  11 +
 .../foo/test/src/foo/RandomTestsH.kt          |  11 +
 .../foo/test/src/foo/RandomTestsI.kt          |  11 +
 .../foo/test/src/foo/RandomTestsJ.kt          |  11 +
 .../foo/test/src/foo/RandomTestsUtils.kt      |  12 +
 .../testing/6-test-group-stealing/build.mill  |  26 ++
 .../6-test-group-stealing/foo/src/foo/Foo.kt  |  11 +
 .../foo/test/src/foo/GroupX1.kt               |  11 +
 .../foo/test/src/foo/GroupX10.kt              |  11 +
 .../foo/test/src/foo/GroupX2.kt               |  11 +
 .../foo/test/src/foo/GroupX3.kt               |  11 +
 .../foo/test/src/foo/GroupX4.kt               |  11 +
 .../foo/test/src/foo/GroupX5.kt               |  11 +
 .../foo/test/src/foo/GroupX6.kt               |  11 +
 .../foo/test/src/foo/GroupX7.kt               |  11 +
 .../foo/test/src/foo/GroupX8.kt               |  11 +
 .../foo/test/src/foo/GroupX9.kt               |  11 +
 .../foo/test/src/foo/GroupY1.kt               |  11 +
 .../foo/test/src/foo/GroupY10.kt              |  11 +
 .../foo/test/src/foo/GroupY2.kt               |  11 +
 .../foo/test/src/foo/GroupY3.kt               |  11 +
 .../foo/test/src/foo/GroupY4.kt               |  11 +
 .../foo/test/src/foo/GroupY5.kt               |  11 +
 .../foo/test/src/foo/GroupY6.kt               |  11 +
 .../foo/test/src/foo/GroupY7.kt               |  11 +
 .../foo/test/src/foo/GroupY8.kt               |  11 +
 .../foo/test/src/foo/GroupY9.kt               |  11 +
 .../foo/test/src/foo/RandomTestsUtils.kt      |  12 +
 .../testing/5-test-stealing/build.mill        |  41 ++
 .../testing/5-test-stealing/foo/src/Foo.scala |   7 +
 .../foo/test/src/RandomTestsA.scala           |   7 +
 .../foo/test/src/RandomTestsB.scala           |   7 +
 .../foo/test/src/RandomTestsC.scala           |   7 +
 .../foo/test/src/RandomTestsD.scala           |   7 +
 .../foo/test/src/RandomTestsE.scala           |   7 +
 .../foo/test/src/RandomTestsF.scala           |   7 +
 .../foo/test/src/RandomTestsG.scala           |   7 +
 .../foo/test/src/RandomTestsH.scala           |   7 +
 .../foo/test/src/RandomTestsI.scala           |   7 +
 .../foo/test/src/RandomTestsJ.scala           |   7 +
 .../foo/test/src/RandomTestsUtils.scala       |  16 +
 .../testing/6-test-group-stealing/build.mill  |  51 +++
 .../6-test-group-stealing/foo/src/Foo.scala   |   7 +
 .../foo/test/src/GroupX1.scala                |   7 +
 .../foo/test/src/GroupX10.scala               |   7 +
 .../foo/test/src/GroupX2.scala                |   7 +
 .../foo/test/src/GroupX3.scala                |   7 +
 .../foo/test/src/GroupX4.scala                |   7 +
 .../foo/test/src/GroupX5.scala                |   7 +
 .../foo/test/src/GroupX6.scala                |   7 +
 .../foo/test/src/GroupX7.scala                |   7 +
 .../foo/test/src/GroupX8.scala                |   7 +
 .../foo/test/src/GroupX9.scala                |   7 +
 .../foo/test/src/GroupY1.scala                |   7 +
 .../foo/test/src/GroupY10.scala               |   7 +
 .../foo/test/src/GroupY2.scala                |   7 +
 .../foo/test/src/GroupY3.scala                |   7 +
 .../foo/test/src/GroupY4.scala                |   7 +
 .../foo/test/src/GroupY5.scala                |   7 +
 .../foo/test/src/GroupY6.scala                |   7 +
 .../foo/test/src/GroupY7.scala                |   7 +
 .../foo/test/src/GroupY8.scala                |   7 +
 .../foo/test/src/GroupY9.scala                |   7 +
 .../foo/test/src/RandomTestsUtils.scala       |  14 +
 main/api/src/mill/api/Ctx.scala               |   6 +-
 .../src/mill/eval/ExecutionContexts.scala     |   9 +-
 scalalib/src/mill/scalalib/TestModule.scala   |  25 +-
 .../src/mill/scalalib/TestModuleUtil.scala    | 381 ++++++++++++++----
 .../scalalib/TestRunnerScalatestTests.scala   |   9 +-
 .../mill/scalalib/TestRunnerTestUtils.scala   |  13 +-
 .../mill/scalalib/TestRunnerUtestTests.scala  |   9 +-
 testrunner/src/mill/testrunner/Model.scala    |   7 +-
 .../src/mill/testrunner/TestRunnerMain0.scala |  32 +-
 .../src/mill/testrunner/TestRunnerUtils.scala | 193 +++++++--
 122 files changed, 1705 insertions(+), 154 deletions(-)
 create mode 100644 example/javalib/testing/5-test-stealing/build.mill
 create mode 100644 example/javalib/testing/5-test-stealing/foo/src/foo/Foo.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsA.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsB.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsC.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsD.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsE.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsF.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsG.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsH.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsI.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsJ.java
 create mode 100644 example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsUtils.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/build.mill
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/src/foo/Foo.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX1.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX10.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX2.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX3.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX4.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX5.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX6.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX7.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX8.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX9.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY1.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY10.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY2.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY3.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY4.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY5.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY6.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY7.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY8.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY9.java
 create mode 100644 example/javalib/testing/6-test-group-stealing/foo/test/src/foo/RandomTestsUtils.java
 create mode 100644 example/kotlinlib/testing/5-test-stealing/build.mill
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/src/foo/Foo.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsA.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsB.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsC.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsD.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsE.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsF.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsG.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsH.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsI.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsJ.kt
 create mode 100644 example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsUtils.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/build.mill
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/src/foo/Foo.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX1.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX10.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX2.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX3.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX4.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX5.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX6.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX7.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX8.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX9.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY1.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY10.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY2.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY3.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY4.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY5.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY6.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY7.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY8.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY9.kt
 create mode 100644 example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/RandomTestsUtils.kt
 create mode 100644 example/scalalib/testing/5-test-stealing/build.mill
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/src/Foo.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsA.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsB.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsC.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsD.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsE.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsF.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsG.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsH.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsI.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsJ.scala
 create mode 100644 example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsUtils.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/build.mill
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/src/Foo.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX1.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX10.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX2.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX3.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX4.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX5.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX6.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX7.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX8.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX9.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY1.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY10.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY2.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY3.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY4.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY5.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY6.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY7.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY8.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY9.scala
 create mode 100644 example/scalalib/testing/6-test-group-stealing/foo/test/src/RandomTestsUtils.scala

diff --git a/.gitignore b/.gitignore
index fdcdd3f8ab7..37eb5b7d54e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -18,4 +18,6 @@ dist/
 build/
 *.bak
 mill-assembly.jar
-mill-native
\ No newline at end of file
+mill-native
+*.mill.orig
+*.mill.rej
\ No newline at end of file
diff --git a/docs/modules/ROOT/pages/javalib/testing.adoc b/docs/modules/ROOT/pages/javalib/testing.adoc
index ff8fde99d47..3a57827d87a 100644
--- a/docs/modules/ROOT/pages/javalib/testing.adoc
+++ b/docs/modules/ROOT/pages/javalib/testing.adoc
@@ -22,6 +22,13 @@ include::partial$example/javalib/testing/3-integration-suite.adoc[]
 
 include::partial$example/javalib/testing/4-test-grouping.adoc[]
 
+== Test Work Stealing Scheduler
+
+include::partial$example/javalib/testing/5-test-stealing.adoc[]
+
+== Test Grouping & Test Work Stealing
+
+include::partial$example/javalib/testing/6-test-group-stealing.adoc[]
 
 == Github Actions Test Reports
 
diff --git a/docs/modules/ROOT/pages/kotlinlib/testing.adoc b/docs/modules/ROOT/pages/kotlinlib/testing.adoc
index 8c4c8500d32..b4477a14781 100644
--- a/docs/modules/ROOT/pages/kotlinlib/testing.adoc
+++ b/docs/modules/ROOT/pages/kotlinlib/testing.adoc
@@ -22,6 +22,13 @@ include::partial$example/kotlinlib/testing/3-integration-suite.adoc[]
 
 include::partial$example/kotlinlib/testing/4-test-grouping.adoc[]
 
+== Test Work Stealing Scheduler
+
+include::partial$example/kotlinlib/testing/5-test-stealing.adoc[]
+
+== Test Grouping & Test Work Stealing
+
+include::partial$example/kotlinlib/testing/6-test-group-stealing.adoc[]
 
 == Github Actions Test Reports
 
diff --git a/docs/modules/ROOT/pages/scalalib/testing.adoc b/docs/modules/ROOT/pages/scalalib/testing.adoc
index a0447d39ce0..99f288a5903 100644
--- a/docs/modules/ROOT/pages/scalalib/testing.adoc
+++ b/docs/modules/ROOT/pages/scalalib/testing.adoc
@@ -22,6 +22,14 @@ include::partial$example/scalalib/testing/3-integration-suite.adoc[]
 
 include::partial$example/scalalib/testing/4-test-grouping.adoc[]
 
+== Test Work Stealing Scheduler
+
+include::partial$example/scalalib/testing/5-test-stealing.adoc[]
+
+== Test Grouping & Test Work Stealing
+
+include::partial$example/scalalib/testing/6-test-group-stealing.adoc[]
+
 == Github Actions Test Reports
 
 If you use Github Actions for CI, you can use https://github.com/mikepenz/action-junit-report in
diff --git a/example/javalib/testing/5-test-stealing/build.mill b/example/javalib/testing/5-test-stealing/build.mill
new file mode 100644
index 00000000000..f4262bcf319
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/build.mill
@@ -0,0 +1,15 @@
+//// SNIPPET:BUILD1
+package build
+import mill._, javalib._
+
+object foo extends JavaModule {
+  object test extends JavaTests {
+    def testFramework = "com.novocode.junit.JUnitFramework"
+    def ivyDeps = Agg(
+      ivy"com.novocode:junit-interface:0.11",
+      ivy"org.mockito:mockito-core:4.6.1"
+    )
+    def testEnableWorkStealing = true
+  }
+}
+//// SNIPPET:END
diff --git a/example/javalib/testing/5-test-stealing/foo/src/foo/Foo.java b/example/javalib/testing/5-test-stealing/foo/src/foo/Foo.java
new file mode 100644
index 00000000000..0a99cb68d67
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/src/foo/Foo.java
@@ -0,0 +1,11 @@
+package foo;
+
+public class Foo {
+  public static void main(String[] args) {
+    System.out.println(greet("World"));
+  }
+
+  public static String greet(String name) {
+    return "Hello " + name;
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsA.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsA.java
new file mode 100644
index 00000000000..75337f0078d
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsA.java
@@ -0,0 +1,11 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsA extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Storm", 38);
+  }
+  // Removed other tests to simplify
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsB.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsB.java
new file mode 100644
index 00000000000..1d4ba5e1fdf
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsB.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsB extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Dakota", 18);
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsC.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsC.java
new file mode 100644
index 00000000000..02918a0a22a
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsC.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsC extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Jordan", 95);
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsD.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsD.java
new file mode 100644
index 00000000000..806dd50550b
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsD.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsD extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Kai", 14);
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsE.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsE.java
new file mode 100644
index 00000000000..e10e4568461
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsE.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsE extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Sage", 28);
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsF.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsF.java
new file mode 100644
index 00000000000..340439deaa3
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsF.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsF extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Winter", 12);
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsG.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsG.java
new file mode 100644
index 00000000000..37fa1bcc5c0
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsG.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsG extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Finn", 45);
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsH.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsH.java
new file mode 100644
index 00000000000..9f568404d8e
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsH.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsH extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Haven", 22);
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsI.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsI.java
new file mode 100644
index 00000000000..44302550c27
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsI.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsI extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Mars", 16);
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsJ.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsJ.java
new file mode 100644
index 00000000000..2fb787905bb
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsJ.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class RandomTestsJ extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Storm", 38);
+  }
+}
diff --git a/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsUtils.java b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsUtils.java
new file mode 100644
index 00000000000..ff21a48b29b
--- /dev/null
+++ b/example/javalib/testing/5-test-stealing/foo/test/src/foo/RandomTestsUtils.java
@@ -0,0 +1,11 @@
+package foo;
+
+import static org.junit.Assert.assertEquals;
+
+public class RandomTestsUtils {
+  protected void testGreeting(String name, int sleepTime) throws Exception {
+    String greeted = Foo.greet(name);
+    Thread.sleep(sleepTime);
+    assertEquals("Hello " + name, greeted);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/build.mill b/example/javalib/testing/6-test-group-stealing/build.mill
new file mode 100644
index 00000000000..2a4a3fd4503
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/build.mill
@@ -0,0 +1,19 @@
+//// SNIPPET:BUILD1
+package build
+import mill._, javalib._
+
+object foo extends JavaModule {
+  object test extends JavaTests {
+    def testFramework = "com.novocode.junit.JUnitFramework"
+    def ivyDeps = Agg(
+      ivy"com.novocode:junit-interface:0.11",
+      ivy"org.mockito:mockito-core:4.6.1"
+    )
+    def testForkGrouping =
+      discoveredTestClasses().groupMapReduce(_.contains("GroupX"))(Seq(_))(_ ++ _).toSeq.sortBy(
+        data => !data._1
+      ).map(_._2)
+    def testEnableWorkStealing = true
+  }
+}
+//// SNIPPET:END
diff --git a/example/javalib/testing/6-test-group-stealing/foo/src/foo/Foo.java b/example/javalib/testing/6-test-group-stealing/foo/src/foo/Foo.java
new file mode 100644
index 00000000000..0a99cb68d67
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/src/foo/Foo.java
@@ -0,0 +1,11 @@
+package foo;
+
+public class Foo {
+  public static void main(String[] args) {
+    System.out.println(greet("World"));
+  }
+
+  public static String greet(String name) {
+    return "Hello " + name;
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX1.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX1.java
new file mode 100644
index 00000000000..22aa90886aa
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX1.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX1 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Aether", 55);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX10.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX10.java
new file mode 100644
index 00000000000..8c53423530e
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX10.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX10 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Echo", 52);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX2.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX2.java
new file mode 100644
index 00000000000..c508fc8befb
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX2.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX2 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Chronos", 35);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX3.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX3.java
new file mode 100644
index 00000000000..39e42f69a39
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX3.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX3 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Fortuna", 25);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX4.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX4.java
new file mode 100644
index 00000000000..5d38ea5d644
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX4.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX4 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Janus", 21);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX5.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX5.java
new file mode 100644
index 00000000000..042a7567ee8
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX5.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX5 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Orion", 95);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX6.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX6.java
new file mode 100644
index 00000000000..0aeeaebc9ea
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX6.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX6 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Perseus", 34);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX7.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX7.java
new file mode 100644
index 00000000000..01372630a40
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX7.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX7 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Selene", 52);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX8.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX8.java
new file mode 100644
index 00000000000..664f2a618f1
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX8.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX8 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Uranus", 25);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX9.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX9.java
new file mode 100644
index 00000000000..fcb065b5158
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupX9.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupX9 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Ymir", 17);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY1.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY1.java
new file mode 100644
index 00000000000..99038cf4088
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY1.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY1 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Hades", 15);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY10.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY10.java
new file mode 100644
index 00000000000..60c5bca3289
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY10.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY10 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Rama", 25);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY2.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY2.java
new file mode 100644
index 00000000000..eb77713cced
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY2.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY2 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Odin", 34);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY3.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY3.java
new file mode 100644
index 00000000000..8b3dc5d8a4c
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY3.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY3 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Ra", 21);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY4.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY4.java
new file mode 100644
index 00000000000..ae82b836aca
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY4.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY4 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Wotan", 95);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY5.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY5.java
new file mode 100644
index 00000000000..2cb091e8d6f
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY5.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY5 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Xiuhtecuhtli", 26);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY6.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY6.java
new file mode 100644
index 00000000000..2788e0bc99c
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY6.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY6 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Baldur", 17);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY7.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY7.java
new file mode 100644
index 00000000000..f8442288ca1
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY7.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY7 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Horus", 34);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY8.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY8.java
new file mode 100644
index 00000000000..e581738bce7
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY8.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY8 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Khonsu", 53);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY9.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY9.java
new file mode 100644
index 00000000000..83f5742bf79
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/GroupY9.java
@@ -0,0 +1,10 @@
+package foo;
+
+import org.junit.Test;
+
+public class GroupY9 extends RandomTestsUtils {
+  @Test
+  public void test1() throws Exception {
+    testGreeting("Minerva", 21);
+  }
+}
diff --git a/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/RandomTestsUtils.java b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/RandomTestsUtils.java
new file mode 100644
index 00000000000..ff21a48b29b
--- /dev/null
+++ b/example/javalib/testing/6-test-group-stealing/foo/test/src/foo/RandomTestsUtils.java
@@ -0,0 +1,11 @@
+package foo;
+
+import static org.junit.Assert.assertEquals;
+
+public class RandomTestsUtils {
+  protected void testGreeting(String name, int sleepTime) throws Exception {
+    String greeted = Foo.greet(name);
+    Thread.sleep(sleepTime);
+    assertEquals("Hello " + name, greeted);
+  }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/build.mill b/example/kotlinlib/testing/5-test-stealing/build.mill
new file mode 100644
index 00000000000..84808520c19
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/build.mill
@@ -0,0 +1,22 @@
+//// SNIPPET:BUILD1
+package build
+import mill._, kotlinlib._
+
+object foo extends KotlinModule {
+
+  def mainClass = Some("foo.FooKt")
+
+  def kotlinVersion = "1.9.24"
+
+  object test extends KotlinTests {
+    def testFramework = "com.github.sbt.junit.jupiter.api.JupiterFramework"
+    def ivyDeps = Agg(
+      ivy"com.github.sbt.junit:jupiter-interface:0.11.4",
+      ivy"io.kotest:kotest-runner-junit5-jvm:5.9.1",
+      ivy"org.mockito.kotlin:mockito-kotlin:5.4.0"
+    )
+
+    def testEnableWorkStealing = true
+  }
+}
+//// SNIPPET:END
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/src/foo/Foo.kt b/example/kotlinlib/testing/5-test-stealing/foo/src/foo/Foo.kt
new file mode 100644
index 00000000000..5d549fb79eb
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/src/foo/Foo.kt
@@ -0,0 +1,11 @@
+package foo
+
+object Foo {
+    @JvmStatic
+    fun main(args: Array<String>) {
+        println(greet("World"))
+    }
+
+    @JvmStatic
+    fun greet(name: String): String = "Hello $name"
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsA.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsA.kt
new file mode 100644
index 00000000000..166d5cf75aa
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsA.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsA : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Storm", 38)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsB.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsB.kt
new file mode 100644
index 00000000000..eb6a1597506
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsB.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsB : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Dakota", 18)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsC.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsC.kt
new file mode 100644
index 00000000000..8c986e46824
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsC.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsC : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Jordan", 95)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsD.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsD.kt
new file mode 100644
index 00000000000..9304dda44cc
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsD.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsD : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Kai", 14)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsE.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsE.kt
new file mode 100644
index 00000000000..55ad80de805
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsE.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsE : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Sage", 28)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsF.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsF.kt
new file mode 100644
index 00000000000..496b0006b8c
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsF.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsF : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Winter", 12)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsG.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsG.kt
new file mode 100644
index 00000000000..8638a5ef1c3
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsG.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsG : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Finn", 45)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsH.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsH.kt
new file mode 100644
index 00000000000..05d1913fc74
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsH.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsH : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Haven", 22)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsI.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsI.kt
new file mode 100644
index 00000000000..56fde3cac20
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsI.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsI : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Mars", 16)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsJ.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsJ.kt
new file mode 100644
index 00000000000..948cfdde5ca
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsJ.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class RandomTestsJ : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Storm", 38)
+    }
+}
diff --git a/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsUtils.kt b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsUtils.kt
new file mode 100644
index 00000000000..42e6839e75d
--- /dev/null
+++ b/example/kotlinlib/testing/5-test-stealing/foo/test/src/foo/RandomTestsUtils.kt
@@ -0,0 +1,12 @@
+package foo
+
+import org.junit.jupiter.api.Assertions.assertEquals
+
+open class RandomTestsUtils {
+    @Throws(Exception::class)
+    protected fun testGreeting(name: String, sleepTime: Int) {
+        val greeted = Foo.greet(name)
+        Thread.sleep(sleepTime.toLong())
+        assertEquals("Hello $name", greeted)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/build.mill b/example/kotlinlib/testing/6-test-group-stealing/build.mill
new file mode 100644
index 00000000000..5c0943c2b91
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/build.mill
@@ -0,0 +1,26 @@
+//// SNIPPET:BUILD1
+package build
+import mill._, kotlinlib._
+
+object foo extends KotlinModule {
+
+  def mainClass = Some("foo.FooKt")
+
+  def kotlinVersion = "1.9.24"
+
+  object test extends KotlinTests {
+    def testFramework = "com.github.sbt.junit.jupiter.api.JupiterFramework"
+    def ivyDeps = Agg(
+      ivy"com.github.sbt.junit:jupiter-interface:0.11.4",
+      ivy"io.kotest:kotest-runner-junit5-jvm:5.9.1",
+      ivy"org.mockito.kotlin:mockito-kotlin:5.4.0"
+    )
+
+    def testForkGrouping =
+      discoveredTestClasses().groupMapReduce(_.contains("GroupX"))(Seq(_))(_ ++ _).toSeq.sortBy(
+        data => !data._1
+      ).map(_._2)
+    def testEnableWorkStealing = true
+  }
+}
+//// SNIPPET:END
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/src/foo/Foo.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/src/foo/Foo.kt
new file mode 100644
index 00000000000..5d549fb79eb
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/src/foo/Foo.kt
@@ -0,0 +1,11 @@
+package foo
+
+object Foo {
+    @JvmStatic
+    fun main(args: Array<String>) {
+        println(greet("World"))
+    }
+
+    @JvmStatic
+    fun greet(name: String): String = "Hello $name"
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX1.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX1.kt
new file mode 100644
index 00000000000..bff63dac124
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX1.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX1 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Aether", 55)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX10.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX10.kt
new file mode 100644
index 00000000000..9d4d6f25608
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX10.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX10 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Echo", 52)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX2.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX2.kt
new file mode 100644
index 00000000000..4f3e49d4738
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX2.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX2 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Chronos", 35)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX3.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX3.kt
new file mode 100644
index 00000000000..1f71a0f25af
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX3.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX3 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Fortuna", 25)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX4.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX4.kt
new file mode 100644
index 00000000000..d76259bca72
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX4.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX4 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Janus", 21)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX5.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX5.kt
new file mode 100644
index 00000000000..284f48f90d1
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX5.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX5 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Orion", 95)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX6.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX6.kt
new file mode 100644
index 00000000000..e6611ea0115
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX6.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX6 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Perseus", 34)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX7.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX7.kt
new file mode 100644
index 00000000000..14eaf3b6e2d
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX7.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX7 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Selene", 52)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX8.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX8.kt
new file mode 100644
index 00000000000..33fa55a3278
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX8.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX8 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Uranus", 25)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX9.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX9.kt
new file mode 100644
index 00000000000..e6d50458025
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupX9.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupX9 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Ymir", 17)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY1.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY1.kt
new file mode 100644
index 00000000000..a6260b4f85a
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY1.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY1 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Hades", 15)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY10.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY10.kt
new file mode 100644
index 00000000000..f5a4e71cd63
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY10.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY10 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Rama", 25)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY2.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY2.kt
new file mode 100644
index 00000000000..b344676c823
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY2.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY2 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Odin", 34)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY3.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY3.kt
new file mode 100644
index 00000000000..d639af9a233
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY3.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY3 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Ra", 21)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY4.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY4.kt
new file mode 100644
index 00000000000..9637ac7b185
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY4.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY4 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Wotan", 95)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY5.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY5.kt
new file mode 100644
index 00000000000..4b23ca15fb0
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY5.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY5 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Xiuhtecuhtli", 26)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY6.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY6.kt
new file mode 100644
index 00000000000..fd4b90fab8e
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY6.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY6 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Baldur", 17)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY7.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY7.kt
new file mode 100644
index 00000000000..4da4051126c
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY7.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY7 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Horus", 34)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY8.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY8.kt
new file mode 100644
index 00000000000..e6f376cad28
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY8.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY8 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Khonsu", 53)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY9.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY9.kt
new file mode 100644
index 00000000000..fec324099c2
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/GroupY9.kt
@@ -0,0 +1,11 @@
+package foo
+
+import org.junit.jupiter.api.Test
+
+class GroupY9 : RandomTestsUtils() {
+    @Test
+    @Throws(Exception::class)
+    fun test1() {
+        testGreeting("Minerva", 21)
+    }
+}
diff --git a/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/RandomTestsUtils.kt b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/RandomTestsUtils.kt
new file mode 100644
index 00000000000..42e6839e75d
--- /dev/null
+++ b/example/kotlinlib/testing/6-test-group-stealing/foo/test/src/foo/RandomTestsUtils.kt
@@ -0,0 +1,12 @@
+package foo
+
+import org.junit.jupiter.api.Assertions.assertEquals
+
+open class RandomTestsUtils {
+    @Throws(Exception::class)
+    protected fun testGreeting(name: String, sleepTime: Int) {
+        val greeted = Foo.greet(name)
+        Thread.sleep(sleepTime.toLong())
+        assertEquals("Hello $name", greeted)
+    }
+}
diff --git a/example/scalalib/testing/5-test-stealing/build.mill b/example/scalalib/testing/5-test-stealing/build.mill
new file mode 100644
index 00000000000..755843f4e3b
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/build.mill
@@ -0,0 +1,41 @@
+// Test stealing is an opt-in, powerful feature that enables parallel test execution.
+// When enabled, Mill automatically distributes your test classes across multiple JVM subprocesses.
+// This is especially useful when you have multiple test classes that can be run in parallel.
+// Work stealing scheduler ensures throughput is maximized: no "slow" tests can block "fast" tests.
+// This feature is expected to be enabled by default in future versions of Mill.
+//
+// Test stealing can be enabled by overriding def testEnableWorkStealing, as demonstrated below.
+
+//// SNIPPET:BUILD1
+package build
+import mill._, scalalib._
+
+object foo extends ScalaModule {
+  def scalaVersion = "2.13.8"
+  object test extends ScalaTests {
+    def ivyDeps = Agg(ivy"com.lihaoyi::utest:0.8.5")
+    def testFramework = "utest.runner.Framework"
+
+    def testEnableWorkStealing = true
+  }
+}
+
+//// SNIPPET:END
+
+/** Usage
+
+> mill -j 3 foo.test
+
+> find out/foo/test/test.dest
+...
+out/foo/test/test.dest/worker-0.log
+out/foo/test/test.dest/worker-0
+out/foo/test/test.dest/worker-1.log
+out/foo/test/test.dest/worker-1
+out/foo/test/test.dest/worker-2.log
+out/foo/test/test.dest/worker-2
+out/foo/test/test.dest/test-classes
+out/foo/test/test.dest/test-report.xml
+...
+
+*/
diff --git a/example/scalalib/testing/5-test-stealing/foo/src/Foo.scala b/example/scalalib/testing/5-test-stealing/foo/src/Foo.scala
new file mode 100644
index 00000000000..386104354fa
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/src/Foo.scala
@@ -0,0 +1,7 @@
+package foo
+object Foo {
+  def main(args: Array[String]): Unit = {
+    println(greet("World"))
+  }
+  def greet(name: String): String = s"Hello $name"
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsA.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsA.scala
new file mode 100644
index 00000000000..5bf186d79b7
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsA.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsA extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Storm", 38) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsB.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsB.scala
new file mode 100644
index 00000000000..2dff6d6de78
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsB.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsB extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Dakota", 18) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsC.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsC.scala
new file mode 100644
index 00000000000..6711d6a6656
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsC.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsC extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Jordan", 95) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsD.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsD.scala
new file mode 100644
index 00000000000..38eab20f7da
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsD.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsD extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Kai", 14) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsE.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsE.scala
new file mode 100644
index 00000000000..8daaa738344
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsE.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsE extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Sage", 28) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsF.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsF.scala
new file mode 100644
index 00000000000..79032b7ba12
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsF.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsF extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Winter", 12) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsG.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsG.scala
new file mode 100644
index 00000000000..449b7991ce5
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsG.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsG extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Finn", 45) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsH.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsH.scala
new file mode 100644
index 00000000000..c2862cecc3c
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsH.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsH extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Haven", 22) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsI.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsI.scala
new file mode 100644
index 00000000000..18901f12053
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsI.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsI extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Mars", 16) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsJ.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsJ.scala
new file mode 100644
index 00000000000..debdad4859d
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsJ.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object RandomTestsJ extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Storm", 38) }
+  }
+}
diff --git a/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsUtils.scala b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsUtils.scala
new file mode 100644
index 00000000000..87adfe5d609
--- /dev/null
+++ b/example/scalalib/testing/5-test-stealing/foo/test/src/RandomTestsUtils.scala
@@ -0,0 +1,16 @@
+package foo
+import utest._
+
+abstract class RandomTestsUtils extends TestSuite {
+
+  // sleepTime try to mimics real-life test time,
+  // sleepTime can be chosen randomly, but test classes should be "slow" (~100ms)
+  // enough so that cluster decide to spawn all available test runner processeses
+  // fail to do this can lead to flakky test.
+  def testGreeting(name: String, sleepTime: Int) = {
+    val greeted = Foo.greet(name)
+    Thread.sleep(sleepTime)
+    assert(greeted == s"Hello $name")
+  }
+
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/build.mill b/example/scalalib/testing/6-test-group-stealing/build.mill
new file mode 100644
index 00000000000..7b4c4136916
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/build.mill
@@ -0,0 +1,51 @@
+// `testEnableWorkStealing` respects `testForkGrouping`, allowing you to use both features in a test module.
+
+//// SNIPPET:BUILD1
+package build
+import mill._, scalalib._
+
+object foo extends ScalaModule {
+  def scalaVersion = "2.13.8"
+  object test extends ScalaTests {
+    def ivyDeps = Agg(ivy"com.lihaoyi::utest:0.8.5")
+    def testFramework = "utest.runner.Framework"
+
+    // Group tests by GroupX and GroupY
+    def testForkGrouping =
+      discoveredTestClasses().groupMapReduce(_.contains("GroupX"))(Seq(_))(_ ++ _).toSeq.sortBy(
+        data => !data._1
+      ).map(_._2)
+    def testEnableWorkStealing = true
+  }
+}
+
+//// SNIPPET:END
+
+/** Usage
+
+> mill -j 4 foo.test
+
+> find out/foo/test/test.dest
+...
+out/foo/test/test.dest/group-0-foo.GroupX1/worker-0.log
+out/foo/test/test.dest/group-0-foo.GroupX1/worker-0
+out/foo/test/test.dest/group-0-foo.GroupX1/worker-1.log
+out/foo/test/test.dest/group-0-foo.GroupX1/worker-1
+out/foo/test/test.dest/group-0-foo.GroupX1/test-classes
+out/foo/test/test.dest/group-1-foo.GroupY1/worker-0.log
+out/foo/test/test.dest/group-1-foo.GroupY1/worker-0
+out/foo/test/test.dest/group-1-foo.GroupY1/worker-1.log
+out/foo/test/test.dest/group-1-foo.GroupY1/worker-1
+out/foo/test/test.dest/group-1-foo.GroupY1/test-classes
+out/foo/test/test.dest/test-report.xml
+...
+
+*/
+
+// This example sets `testForkGrouping` to group test classes into two categories: `GroupX` and `GroupY`.
+// Additionally, `testEnableWorkStealing` is enabled.
+// Mill ensures each subprocess exclusively steals and runs tests from either `GroupX` or `GroupY`, preventing them from mixing.
+// Test classes from `GroupX` and `GroupY` will never share the same test runner.
+//
+// This is useful when you have incompatible tests that cannot run within the same JVM.
+// Test Grouping combined with Test Stealing Scheduler maintains their isolation while maximizing performance through parallel test execution.
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/src/Foo.scala b/example/scalalib/testing/6-test-group-stealing/foo/src/Foo.scala
new file mode 100644
index 00000000000..386104354fa
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/src/Foo.scala
@@ -0,0 +1,7 @@
+package foo
+object Foo {
+  def main(args: Array[String]): Unit = {
+    println(greet("World"))
+  }
+  def greet(name: String): String = s"Hello $name"
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX1.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX1.scala
new file mode 100644
index 00000000000..1b483ba1a38
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX1.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX1 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Aether", 55) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX10.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX10.scala
new file mode 100644
index 00000000000..7fef760a674
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX10.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX10 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Echo", 52) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX2.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX2.scala
new file mode 100644
index 00000000000..448943c5ea4
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX2.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX2 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Chronos", 35) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX3.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX3.scala
new file mode 100644
index 00000000000..a6b2268a6ab
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX3.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX3 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Fortuna", 25) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX4.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX4.scala
new file mode 100644
index 00000000000..b67e2f8365b
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX4.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX4 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Janus", 21) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX5.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX5.scala
new file mode 100644
index 00000000000..44d42c80d25
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX5.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX5 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Orion", 95) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX6.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX6.scala
new file mode 100644
index 00000000000..ec92a4c27e3
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX6.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX6 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Perseus", 34) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX7.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX7.scala
new file mode 100644
index 00000000000..68983efe882
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX7.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX7 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Selene", 52) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX8.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX8.scala
new file mode 100644
index 00000000000..85d4a1721a6
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX8.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX8 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Uranus", 25) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX9.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX9.scala
new file mode 100644
index 00000000000..84518f008c8
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupX9.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupX9 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Ymir", 17) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY1.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY1.scala
new file mode 100644
index 00000000000..448f840aad3
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY1.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY1 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Hades", 15) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY10.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY10.scala
new file mode 100644
index 00000000000..ca7553275e1
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY10.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY10 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Rama", 25) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY2.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY2.scala
new file mode 100644
index 00000000000..f1c66479a3c
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY2.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY2 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Odin", 34) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY3.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY3.scala
new file mode 100644
index 00000000000..eed43b1aee7
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY3.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY3 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Ra", 21) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY4.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY4.scala
new file mode 100644
index 00000000000..baa86a70269
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY4.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY4 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Wotan", 95) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY5.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY5.scala
new file mode 100644
index 00000000000..6c05f52d644
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY5.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY5 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Xiuhtecuhtli", 26) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY6.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY6.scala
new file mode 100644
index 00000000000..536292adc60
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY6.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY6 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Baldur", 17) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY7.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY7.scala
new file mode 100644
index 00000000000..d2f761c3eda
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY7.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY7 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Horus", 34) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY8.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY8.scala
new file mode 100644
index 00000000000..fdc676a27b0
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY8.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY8 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Khonsu", 53) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY9.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY9.scala
new file mode 100644
index 00000000000..0c4ac5a14ae
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/GroupY9.scala
@@ -0,0 +1,7 @@
+package foo
+import utest._
+object GroupY9 extends RandomTestsUtils {
+  def tests = Tests {
+    test("test1") { testGreeting("Minerva", 21) }
+  }
+}
diff --git a/example/scalalib/testing/6-test-group-stealing/foo/test/src/RandomTestsUtils.scala b/example/scalalib/testing/6-test-group-stealing/foo/test/src/RandomTestsUtils.scala
new file mode 100644
index 00000000000..49cb7a65a86
--- /dev/null
+++ b/example/scalalib/testing/6-test-group-stealing/foo/test/src/RandomTestsUtils.scala
@@ -0,0 +1,14 @@
+package foo
+import utest._
+
+abstract class RandomTestsUtils extends TestSuite {
+  // sleepTime try to mimics real-life test time,
+  // sleepTime can be chosen randomly, but test classes should be "slow" (~100ms)
+  // enough so that cluster decide to spawn all available test runner processeses
+  // fail to do this can lead to flakky test.
+  def testGreeting(name: String, sleepTime: Int): Unit = {
+    val greeted = Foo.greet(name)
+    Thread.sleep(sleepTime)
+    assert(greeted == s"Hello $name")
+  }
+}
diff --git a/main/api/src/mill/api/Ctx.scala b/main/api/src/mill/api/Ctx.scala
index 8bba02268e1..f42915cb336 100644
--- a/main/api/src/mill/api/Ctx.scala
+++ b/main/api/src/mill/api/Ctx.scala
@@ -161,9 +161,13 @@ object Ctx {
        *                terminal prompt to display what this future is currently computing.
        * @param t The body of the async future
        */
-      def async[T](dest: os.Path, key: String, message: String)(t: => T)(implicit
+      def async[T](dest: os.Path, key: String, message: String, t: Logger => T)(implicit
           ctx: mill.api.Ctx
       ): Future[T]
+
+      def async[T](dest: os.Path, key: String, message: String)(t: => T)(implicit
+          ctx: mill.api.Ctx
+      ): Future[T] = async(dest, key, message, _ => t)(ctx)
     }
 
     trait Impl extends Api with ExecutionContext with AutoCloseable {
diff --git a/main/eval/src/mill/eval/ExecutionContexts.scala b/main/eval/src/mill/eval/ExecutionContexts.scala
index 0384fe3477f..6fff3eec821 100644
--- a/main/eval/src/mill/eval/ExecutionContexts.scala
+++ b/main/eval/src/mill/eval/ExecutionContexts.scala
@@ -5,6 +5,7 @@ import os.Path
 import scala.concurrent.{Await, Future}
 import scala.concurrent.duration.Duration
 import java.util.concurrent.{ExecutorService, LinkedBlockingQueue, ThreadPoolExecutor, TimeUnit}
+import mill.api.Logger
 
 private object ExecutionContexts {
 
@@ -19,10 +20,10 @@ private object ExecutionContexts {
     def reportFailure(cause: Throwable): Unit = {}
     def close(): Unit = () // do nothing
 
-    def async[T](dest: Path, key: String, message: String)(t: => T)(implicit
+    def async[T](dest: Path, key: String, message: String, t: Logger => T)(implicit
         ctx: mill.api.Ctx
     ): Future[T] =
-      Future.successful(t)
+      Future.successful(t(ctx.log))
   }
 
   /**
@@ -81,7 +82,7 @@ private object ExecutionContexts {
      * folder [[dest]] and duplicates the logging streams to [[dest]].log while evaluating
      * [[t]], to avoid conflict with other tasks that may be running concurrently
      */
-    def async[T](dest: Path, key: String, message: String)(t: => T)(implicit
+    def async[T](dest: Path, key: String, message: String, t: Logger => T)(implicit
         ctx: mill.api.Ctx
     ): Future[T] = {
       val logger = ctx.log.subLogger(dest / os.up / s"${dest.last}.log", key, message)
@@ -99,7 +100,7 @@ private object ExecutionContexts {
         logger.withPrompt {
           os.dynamicPwdFunction.withValue(() => makeDest()) {
             mill.api.SystemStreams.withStreams(logger.systemStreams) {
-              t
+              t(logger)
             }
           }
         }
diff --git a/scalalib/src/mill/scalalib/TestModule.scala b/scalalib/src/mill/scalalib/TestModule.scala
index 476cbe165bd..4c5415f656e 100644
--- a/scalalib/src/mill/scalalib/TestModule.scala
+++ b/scalalib/src/mill/scalalib/TestModule.scala
@@ -96,15 +96,24 @@ trait TestModule
   }
 
   /**
-   * How the test classes in this module will be split into multiple JVM processes
-   * and run in parallel during testing. Defaults to all of them running in one process
-   * sequentially, but can be overridden to split them into separate groups that run
-   * in parallel.
+   * How the test classes in this module will be split.
+   * Test classes from different groups are ensured to never
+   * run on the same JVM process, and therefore can be run in parallel.
+   * When used in combination with [[testEnableWorkStealing]],
+   * every JVM test running process will guarantee to never steal tests
+   * from different test groups.
    */
   def testForkGrouping: T[Seq[Seq[String]]] = Task {
     Seq(discoveredTestClasses())
   }
 
+  /**
+   * Whether to use the test stealing scheduler to run tests in multiple JVM processes.
+   * When used in combination with [[testForkGrouping]], every JVM test running process
+   * will guarantee to never steal tests from different test groups.
+   */
+  def testEnableWorkStealing: T[Boolean] = T(false)
+
   /**
    * Discovers and runs the module's tests in a subprocess, reporting the
    * results to the console.
@@ -157,7 +166,7 @@ trait TestModule
         colored = Task.log.colored,
         testCp = testClasspath().map(_.path),
         home = Task.home,
-        globSelectors = selectors
+        globSelectors = Left(selectors)
       )
 
       val argsFile = Task.dest / "testargs"
@@ -190,7 +199,7 @@ trait TestModule
       globSelectors: Task[Seq[String]]
   ): Task[(String, Seq[TestResult])] =
     Task.Anon {
-      TestModuleUtil.runTests(
+      val testModuleUtil = new TestModuleUtil(
         testUseArgsFile(),
         forkArgs(),
         globSelectors(),
@@ -206,8 +215,10 @@ trait TestModule
         testSandboxWorkingDir(),
         forkWorkingDir(),
         testReportXml(),
-        zincWorker().javaHome().map(_.path)
+        zincWorker().javaHome().map(_.path),
+        testEnableWorkStealing()
       )
+      testModuleUtil.runTests()
     }
 
   /**
diff --git a/scalalib/src/mill/scalalib/TestModuleUtil.scala b/scalalib/src/mill/scalalib/TestModuleUtil.scala
index e0527ff57f1..367508b6766 100644
--- a/scalalib/src/mill/scalalib/TestModuleUtil.scala
+++ b/scalalib/src/mill/scalalib/TestModuleUtil.scala
@@ -11,77 +11,43 @@ import java.time.format.DateTimeFormatter
 import java.time.temporal.ChronoUnit
 import java.time.{Instant, LocalDateTime, ZoneId}
 import scala.xml.Elem
-
-private[scalalib] object TestModuleUtil {
-  def runTests(
-      useArgsFile: Boolean,
-      forkArgs: Seq[String],
-      selectors: Seq[String],
-      scalalibClasspath: Agg[PathRef],
-      resources: Seq[PathRef],
-      testFramework: String,
-      runClasspath: Seq[PathRef],
-      testClasspath: Seq[PathRef],
-      args: Seq[String],
-      testClassLists: Seq[Seq[String]],
-      testrunnerEntrypointClasspath: Agg[PathRef],
-      forkEnv: Map[String, String],
-      testSandboxWorkingDir: Boolean,
-      forkWorkingDir: os.Path,
-      testReportXml: Option[String],
-      javaHome: Option[os.Path]
-  )(implicit ctx: mill.api.Ctx) = {
-
-    val (jvmArgs, props: Map[String, String]) = loadArgsAndProps(useArgsFile, forkArgs)
-
-    val testRunnerClasspathArg = scalalibClasspath
-      .map(_.path.toNIO.toUri.toURL)
-      .mkString(",")
-
-    val resourceEnv = Map(
-      EnvVars.MILL_TEST_RESOURCE_DIR -> resources.map(_.path).mkString(";"),
-      EnvVars.MILL_WORKSPACE_ROOT -> Task.workspace.toString
-    )
-
-    def runTestRunnerSubprocess(selectors2: Seq[String], base: os.Path) = {
-      val outputPath = base / "out.json"
-      val testArgs = TestArgs(
-        framework = testFramework,
-        classpath = runClasspath.map(_.path),
-        arguments = args,
-        sysProps = props,
-        outputPath = outputPath,
-        colored = Task.log.colored,
-        testCp = testClasspath.map(_.path),
-        home = Task.home,
-        globSelectors = selectors2
-      )
-
-      val argsFile = base / "testargs"
-      val sandbox = base / "sandbox"
-      os.write(argsFile, upickle.default.write(testArgs), createFolders = true)
-
-      os.makeDir.all(sandbox)
-
-      Jvm.callProcess(
-        mainClass = "mill.testrunner.entrypoint.TestRunnerMain",
-        classPath = (runClasspath ++ testrunnerEntrypointClasspath).map(_.path),
-        jvmArgs = jvmArgs,
-        env = forkEnv ++ resourceEnv,
-        mainArgs = Seq(testRunnerClasspathArg, argsFile.toString),
-        cwd = if (testSandboxWorkingDir) sandbox else forkWorkingDir,
-        cpPassingJarPath = Option.when(useArgsFile)(
-          os.temp(prefix = "run-", suffix = ".jar", deleteOnExit = false)
-        ),
-        javaHome = javaHome,
-        stdin = os.Inherit,
-        stdout = os.Inherit
-      )
-
-      if (!os.exists(outputPath)) Left(s"Test reporting Failed: ${outputPath} does not exist")
-      else Right(upickle.default.read[(String, Seq[TestResult])](ujson.read(outputPath.toIO)))
-    }
-
+import scala.collection.mutable
+import mill.api.Logger
+import java.util.concurrent.Executors
+
+private final class TestModuleUtil(
+    useArgsFile: Boolean,
+    forkArgs: Seq[String],
+    selectors: Seq[String],
+    scalalibClasspath: Agg[PathRef],
+    resources: Seq[PathRef],
+    testFramework: String,
+    runClasspath: Seq[PathRef],
+    testClasspath: Seq[PathRef],
+    args: Seq[String],
+    testClassLists: Seq[Seq[String]],
+    testrunnerEntrypointClasspath: Agg[PathRef],
+    forkEnv: Map[String, String],
+    testSandboxWorkingDir: Boolean,
+    forkWorkingDir: os.Path,
+    testReportXml: Option[String],
+    javaHome: Option[os.Path],
+    testEnableWorkStealing: Boolean
+)(implicit ctx: mill.api.Ctx) {
+
+  private val (jvmArgs, props: Map[String, String]) =
+    TestModuleUtil.loadArgsAndProps(useArgsFile, forkArgs)
+
+  private val testRunnerClasspathArg = scalalibClasspath
+    .map(_.path.toNIO.toUri.toURL)
+    .mkString(",")
+
+  private val resourceEnv = Map(
+    EnvVars.MILL_TEST_RESOURCE_DIR -> resources.map(_.path).mkString(";"),
+    EnvVars.MILL_WORKSPACE_ROOT -> Task.workspace.toString
+  )
+
+  def runTests(): Result[(String, Seq[TestResult])] = {
     val globFilter = TestRunnerUtils.globFilter(selectors)
 
     def doesNotMatchError = Result.Failure(
@@ -133,18 +99,89 @@ private[scalalib] object TestModuleUtil {
       }
     if (selectors.nonEmpty && filteredClassLists.isEmpty) throw doesNotMatchError
 
-    val subprocessResult: Either[String, (String, Seq[TestResult])] = filteredClassLists match {
+    val result = if (testEnableWorkStealing) {
+      runTestStealingScheduler(filteredClassLists)
+    } else {
+      runTestDefault(filteredClassLists)
+    }
+
+    result match {
+      case Left(errMsg) => Result.Failure(errMsg)
+      case Right((doneMsg, results)) =>
+        if (results.isEmpty && selectors.nonEmpty) throw doesNotMatchError
+        try TestModuleUtil.handleResults(doneMsg, results, Task.ctx(), testReportXml)
+        catch {
+          case e: Throwable => Result.Failure("Test reporting failed: " + e)
+        }
+    }
+  }
+
+  private def callTestRunnerSubprocess(
+      baseFolder: os.Path,
+      // either:
+      // - Left(selectors: Seq[String]): - list of glob selectors to feed to the test runner directly.
+      // - Right((testClassesFolder: os.Path, stealFolder: os.Path)): - folder containing test classes for test runner to steal from, and the stealer's base folder.
+      selector: Either[Seq[String], (os.Path, os.Path)]
+  )(implicit ctx: mill.api.Ctx) = {
+    os.makeDir.all(baseFolder)
+
+    val outputPath = baseFolder / "out.json"
+    val testArgs = TestArgs(
+      framework = testFramework,
+      classpath = runClasspath.map(_.path),
+      arguments = args,
+      sysProps = props,
+      outputPath = outputPath,
+      colored = Task.log.colored,
+      testCp = testClasspath.map(_.path),
+      home = Task.home,
+      globSelectors = selector
+    )
+
+    val argsFile = baseFolder / "testargs"
+    val sandbox = baseFolder / "sandbox"
+    os.write(argsFile, upickle.default.write(testArgs), createFolders = true)
+
+    os.makeDir.all(sandbox)
+
+    Jvm.callProcess(
+      mainClass = "mill.testrunner.entrypoint.TestRunnerMain",
+      classPath = (runClasspath ++ testrunnerEntrypointClasspath).map(_.path),
+      jvmArgs = jvmArgs,
+      env = forkEnv ++ resourceEnv,
+      mainArgs = Seq(testRunnerClasspathArg, argsFile.toString),
+      cwd = if (testSandboxWorkingDir) sandbox else forkWorkingDir,
+      cpPassingJarPath = Option.when(useArgsFile)(
+        os.temp(prefix = "run-", suffix = ".jar", deleteOnExit = false)
+      ),
+      javaHome = javaHome,
+      stdin = os.Inherit,
+      stdout = os.Inherit
+    )
+
+    if (!os.exists(outputPath)) Left(s"Test reporting Failed: ${outputPath} does not exist")
+    else Right(upickle.default.read[(String, Seq[TestResult])](ujson.read(outputPath.toIO)))
+  }
+
+  private def runTestDefault(
+      filteredClassLists: Seq[Seq[String]]
+  )(implicit ctx: mill.api.Ctx) = {
+
+    val subprocessResult = filteredClassLists match {
       // When no tests at all are discovered, run at least one test JVM
       // process to go through the test framework setup/teardown logic
-      case Nil => runTestRunnerSubprocess(Nil, Task.dest)
-      case Seq(singleTestClassList) => runTestRunnerSubprocess(singleTestClassList, Task.dest)
+      case Nil => callTestRunnerSubprocess(Task.dest, Left(Nil))
+      case Seq(singleTestClassList) =>
+        callTestRunnerSubprocess(Task.dest, Left(singleTestClassList))
       case multipleTestClassLists =>
         val maxLength = multipleTestClassLists.length.toString.length
         val futures = multipleTestClassLists.zipWithIndex.map { case (testClassList, i) =>
           val groupPromptMessage = testClassList match {
             case Seq(single) => single
             case multiple =>
-              collapseTestClassNames(multiple).mkString(", ") + s", ${multiple.length} suites"
+              TestModuleUtil.collapseTestClassNames(
+                multiple
+              ).mkString(", ") + s", ${multiple.length} suites"
           }
 
           val paddedIndex = mill.util.Util.leftPad(i.toString, maxLength, '0')
@@ -155,7 +192,7 @@ private[scalalib] object TestModuleUtil {
           }
 
           Task.fork.async(Task.dest / folderName, paddedIndex, groupPromptMessage) {
-            (folderName, runTestRunnerSubprocess(testClassList, Task.dest / folderName))
+            (folderName, callTestRunnerSubprocess(Task.dest / folderName, Left(testClassList)))
           }
         }
 
@@ -170,18 +207,194 @@ private[scalalib] object TestModuleUtil {
         else Right((rights.map(_._1).mkString("\n"), rights.flatMap(_._2)))
     }
 
-    subprocessResult match {
-      case Left(errMsg) => Result.Failure(errMsg)
-      case Right((doneMsg, results)) =>
-        if (results.isEmpty && selectors.nonEmpty) throw doesNotMatchError
-        try handleResults(doneMsg, results, Task.ctx(), testReportXml)
-        catch {
-          case e: Throwable => Result.Failure("Test reporting failed: " + e)
+    subprocessResult
+  }
+
+  private def runTestStealingScheduler(
+      filteredClassLists: Seq[Seq[String]]
+  )(implicit ctx: mill.api.Ctx) = {
+
+    val workerStatusMap = new java.util.concurrent.ConcurrentHashMap[os.Path, String => Unit]()
+
+    def prepareTestClassesFolder(selectors2: Seq[String], base: os.Path): os.Path = {
+      // test-classes folder is used to store the test classes for the children test runners to steal from
+      val testClassesFolder = base / "test-classes"
+      os.makeDir.all(testClassesFolder)
+      selectors2.zipWithIndex.foreach { case (s, i) =>
+        os.write.over(testClassesFolder / s, Array.empty[Byte])
+      }
+      testClassesFolder
+    }
+
+    def runTestRunnerSubprocess(
+        base: os.Path,
+        testClassesFolder: os.Path,
+        force: Boolean,
+        logger: Logger
+    ) = {
+      // Check if we really need to spawn a new runner
+      if (force || os.list(testClassesFolder).nonEmpty) {
+        val stealFolder = base / "steal"
+        os.makeDir.all(stealFolder)
+        // steal.log file will be appended by the runner with the stolen test class's name
+        // it can be used to check the order of test classes of the runner
+        val stealLog = stealFolder / os.up / s"${stealFolder.last}.log"
+        os.write.over(stealLog, Array.empty[Byte])
+        workerStatusMap.put(stealLog, logger.ticker)
+        val result = callTestRunnerSubprocess(base, Right(testClassesFolder -> stealFolder))
+        workerStatusMap.remove(stealLog)
+        Some(result)
+      } else {
+        None
+      }
+    }
+
+    val groupFolderData = filteredClassLists match {
+      case Nil => Seq((Task.dest, prepareTestClassesFolder(Nil, Task.dest), 0))
+      case Seq(singleTestClassList) =>
+        Seq((
+          Task.dest,
+          prepareTestClassesFolder(singleTestClassList, Task.dest),
+          singleTestClassList.length
+        ))
+      case multipleTestClassLists =>
+        val maxLength = multipleTestClassLists.length.toString.length
+        multipleTestClassLists.zipWithIndex.map { case (testClassList, i) =>
+          val paddedIndex = mill.util.Util.leftPad(i.toString, maxLength, '0')
+          val folderName = testClassList match {
+            case Seq(single) => single
+            case multiple =>
+              s"group-$paddedIndex-${multiple.head}"
+          }
+
+          (
+            Task.dest / folderName,
+            prepareTestClassesFolder(testClassList, Task.dest / folderName),
+            testClassList.length
+          )
+        }
+    }
+
+    val jobs = Task.ctx() match {
+      case j: Ctx.Jobs => j.jobs
+      case _ => 1
+    }
+
+    val maxProcessLength = jobs.toString.length
+    val groupLength = groupFolderData.length
+    val maxGroupLength = groupLength.toString.length
+
+    // We got "--jobs" threads, and "groupLength" test groups, so we will spawn at most jobs * groupLength runners here
+    // In most case, this is more than necessary, and runner creation is expensive,
+    // but we have a check for non-empty test-classes folder before really spawning a new runner, so in practice the overhead is low
+    val subprocessFutures = groupFolderData match {
+      case Seq(singleGroupFolderData) =>
+        val (groupFolder, testClassesFolder, numTests) = singleGroupFolderData
+        val groupName = groupFolder.last
+        for (processIndex <- 0 until Math.max(Math.min(jobs, numTests), 1)) yield {
+          val paddedProcessIndex =
+            mill.util.Util.leftPad(processIndex.toString, maxProcessLength, '0')
+          val processFolder = groupFolder / s"worker-$paddedProcessIndex"
+          Task.fork.async(
+            processFolder,
+            paddedProcessIndex,
+            s"worker-$paddedProcessIndex",
+            logger =>
+              // force run when processIndex == 0 (first subprocess), even if there are no tests to run
+              // to force the process to go through the test framework setup/teardown logic
+              groupName -> runTestRunnerSubprocess(
+                processFolder,
+                testClassesFolder,
+                force = processIndex == 0,
+                logger
+              )
+          )
+        }
+      case multipleGroupFolderData =>
+        for {
+          ((groupFolder, testClassesFolder, numTests), groupIndex) <- groupFolderData.zipWithIndex
+          // Don't have re-calculate for every processes
+          groupName = groupFolder.last
+          paddedGroupIndex = mill.util.Util.leftPad(groupIndex.toString, maxGroupLength, '0')
+          processIndex <- 0 until Math.max(Math.min(jobs, numTests), 1)
+        } yield {
+          val paddedProcessIndex =
+            mill.util.Util.leftPad(processIndex.toString, maxProcessLength, '0')
+          val processFolder = groupFolder / s"worker-$paddedProcessIndex"
+
+          Task.fork.async(
+            processFolder,
+            s"${paddedGroupIndex}-${paddedProcessIndex}",
+            s"worker-${paddedGroupIndex}-${paddedProcessIndex}",
+            logger =>
+              // force run when processIndex == 0 (first subprocess), even if there are no tests to run
+              // to force the process to go through the test framework setup/teardown logic
+              groupName -> runTestRunnerSubprocess(
+                processFolder,
+                testClassesFolder,
+                force = processIndex == 0,
+                logger
+              )
+          )
         }
     }
+
+    val executor = Executors.newScheduledThreadPool(1)
+    val outputs =
+      try {
+        // Periodically check the stealLog file of every runner, and tick the executing test name
+        executor.scheduleWithFixedDelay(
+          () => {
+            workerStatusMap.forEach { (stealLog, callback) =>
+              {
+                try {
+                  // the last one is always the latest
+                  os.read.lines(stealLog).lastOption.foreach(callback)
+                } finally ()
+              }
+            }
+          },
+          0,
+          1,
+          java.util.concurrent.TimeUnit.SECONDS
+        )
+
+        Task.fork.awaitAll(subprocessFutures)
+      } finally {
+        executor.shutdown()
+      }
+
+    val subprocessResult = {
+      val failMap = mutable.Map.empty[String, String]
+      val successMap = mutable.Map.empty[String, (String, Seq[TestResult])]
+
+      outputs.foreach {
+        case (name, Some(Left(v))) => failMap.updateWith(name) {
+            case Some(old) => Some(old + " " + v)
+            case None => Some(v)
+          }
+        case (name, Some(Right((msg, results)))) => successMap.updateWith(name) {
+            case Some((oldMsg, oldResults)) => Some((oldMsg + " " + msg, oldResults ++ results))
+            case None => Some((msg, results))
+          }
+        case _ => ()
+      }
+
+      if (failMap.nonEmpty) {
+        Left(failMap.values.mkString("\n"))
+      } else {
+        Right((successMap.values.map(_._1).mkString("\n"), successMap.values.flatMap(_._2).toSeq))
+      }
+    }
+
+    subprocessResult
   }
 
-  private def loadArgsAndProps(useArgsFile: Boolean, forkArgs: Seq[String]) = {
+}
+
+private[scalalib] object TestModuleUtil {
+
+  private[scalalib] def loadArgsAndProps(useArgsFile: Boolean, forkArgs: Seq[String]) = {
     if (useArgsFile) {
       val (props, jvmArgs) = forkArgs.partition(_.startsWith("-D"))
       val sysProps =
diff --git a/scalalib/test/src/mill/scalalib/TestRunnerScalatestTests.scala b/scalalib/test/src/mill/scalalib/TestRunnerScalatestTests.scala
index 0b92209cfa2..7c439fa4674 100644
--- a/scalalib/test/src/mill/scalalib/TestRunnerScalatestTests.scala
+++ b/scalalib/test/src/mill/scalalib/TestRunnerScalatestTests.scala
@@ -33,7 +33,8 @@ object TestRunnerScalatestTests extends TestSuite {
         Map(
           // No test grouping is triggered because we only run one test class
           testrunner.scalatest -> Set("out.json", "sandbox", "test-report.xml", "testargs"),
-          testrunnerGrouping.scalatest -> Set("out.json", "sandbox", "test-report.xml", "testargs")
+          testrunnerGrouping.scalatest -> Set("out.json", "sandbox", "test-report.xml", "testargs"),
+          testrunnerWorkStealing.scalatest -> Set("worker-0", "test-classes", "test-report.xml")
         )
       )
 
@@ -47,7 +48,8 @@ object TestRunnerScalatestTests extends TestSuite {
             "group-0-mill.scalalib.ScalaTestSpec",
             "mill.scalalib.ScalaTestSpec3",
             "test-report.xml"
-          )
+          ),
+          testrunnerWorkStealing.scalatest -> Set("worker-0", "test-classes", "test-report.xml")
         )
       )
       test("include") - tester.testOnly(
@@ -79,7 +81,8 @@ object TestRunnerScalatestTests extends TestSuite {
             "group-0-mill.scalalib.ScalaTestSpec",
             "mill.scalalib.ScalaTestSpec3",
             "test-report.xml"
-          )
+          ),
+          testrunnerWorkStealing.scalatest -> Set("worker-0", "test-classes", "test-report.xml")
         )
       )
       test("includeAndExclude") - tester.testOnly0 { (eval, mod) =>
diff --git a/scalalib/test/src/mill/scalalib/TestRunnerTestUtils.scala b/scalalib/test/src/mill/scalalib/TestRunnerTestUtils.scala
index 06a6eca9f19..884e95d3115 100644
--- a/scalalib/test/src/mill/scalalib/TestRunnerTestUtils.scala
+++ b/scalalib/test/src/mill/scalalib/TestRunnerTestUtils.scala
@@ -14,18 +14,27 @@ import scala.xml.{Elem, NodeSeq, XML}
 object TestRunnerTestUtils {
   object testrunner extends TestRunnerTestModule {
     def computeTestForkGrouping(x: Seq[String]) = Seq(x)
+    def enableWorkStealing = false
   }
 
   object testrunnerGrouping extends TestRunnerTestModule {
     def computeTestForkGrouping(x: Seq[String]) = x.sorted.grouped(2).toSeq
+    def enableWorkStealing = false
+  }
+
+  object testrunnerWorkStealing extends TestRunnerTestModule {
+    def computeTestForkGrouping(x: Seq[String]) = Seq(x)
+    def enableWorkStealing = true
   }
 
   trait TestRunnerTestModule extends TestBaseModule with ScalaModule {
     def computeTestForkGrouping(x: Seq[String]): Seq[Seq[String]]
+    def enableWorkStealing: Boolean
     def scalaVersion = sys.props.getOrElse("TEST_SCALA_2_13_VERSION", ???)
 
     object utest extends ScalaTests with TestModule.Utest {
       override def testForkGrouping = computeTestForkGrouping(discoveredTestClasses())
+      override def testEnableWorkStealing = enableWorkStealing
       override def ivyDeps = Task {
         super.ivyDeps() ++ Agg(
           ivy"com.lihaoyi::utest:${sys.props.getOrElse("TEST_UTEST_VERSION", ???)}"
@@ -35,6 +44,7 @@ object TestRunnerTestUtils {
 
     object scalatest extends ScalaTests with TestModule.ScalaTest {
       override def testForkGrouping = computeTestForkGrouping(discoveredTestClasses())
+      override def testEnableWorkStealing = enableWorkStealing
       override def ivyDeps = Task {
         super.ivyDeps() ++ Agg(
           ivy"org.scalatest::scalatest:${sys.props.getOrElse("TEST_SCALATEST_VERSION", ???)}"
@@ -62,6 +72,7 @@ object TestRunnerTestUtils {
 
     object ziotest extends ScalaTests with TestModule.ZioTest {
       override def testForkGrouping = computeTestForkGrouping(discoveredTestClasses())
+      override def testEnableWorkStealing = enableWorkStealing
       override def ivyDeps = Task {
         super.ivyDeps() ++ Agg(
           ivy"dev.zio::zio-test:${sys.props.getOrElse("TEST_ZIOTEST_VERSION", ???)}",
@@ -75,7 +86,7 @@ object TestRunnerTestUtils {
 
   class TestOnlyTester(m: TestRunnerTestModule => TestModule) {
     def testOnly0(f: (UnitTester, TestRunnerTestModule) => Unit) = {
-      for (mod <- Seq(testrunner, testrunnerGrouping)) {
+      for (mod <- Seq(testrunner, testrunnerGrouping, testrunnerWorkStealing)) {
         UnitTester(mod, resourcePath).scoped { eval => f(eval, mod) }
       }
     }
diff --git a/scalalib/test/src/mill/scalalib/TestRunnerUtestTests.scala b/scalalib/test/src/mill/scalalib/TestRunnerUtestTests.scala
index e43af5863c2..697f63b1a79 100644
--- a/scalalib/test/src/mill/scalalib/TestRunnerUtestTests.scala
+++ b/scalalib/test/src/mill/scalalib/TestRunnerUtestTests.scala
@@ -38,7 +38,8 @@ object TestRunnerUtestTests extends TestSuite {
         Map(
           testrunner.utest -> Set("out.json", "sandbox", "test-report.xml", "testargs"),
           // When there is only one test group with test classes, we do not put it in a subfolder
-          testrunnerGrouping.utest -> Set("out.json", "sandbox", "test-report.xml", "testargs")
+          testrunnerGrouping.utest -> Set("out.json", "sandbox", "test-report.xml", "testargs"),
+          testrunnerWorkStealing.utest -> Set("worker-0", "test-classes", "test-report.xml")
         )
       )
       test("multi") - tester.testOnly(
@@ -52,7 +53,8 @@ object TestRunnerUtestTests extends TestSuite {
             "mill.scalalib.BarTests",
             "mill.scalalib.FoobarTests",
             "test-report.xml"
-          )
+          ),
+          testrunnerWorkStealing.utest -> Set("worker-0", "test-classes", "test-report.xml")
         )
       )
       test("all") - tester.testOnly(
@@ -67,7 +69,8 @@ object TestRunnerUtestTests extends TestSuite {
             "group-0-mill.scalalib.BarTests",
             "mill.scalalib.FoobarTests",
             "test-report.xml"
-          )
+          ),
+          testrunnerWorkStealing.utest -> Set("worker-0", "test-classes", "test-report.xml")
         )
       )
       test("noMatch") - tester.testOnly0 { (eval, mod) =>
diff --git a/testrunner/src/mill/testrunner/Model.scala b/testrunner/src/mill/testrunner/Model.scala
index 20fb5472b8d..7ae41bdac97 100644
--- a/testrunner/src/mill/testrunner/Model.scala
+++ b/testrunner/src/mill/testrunner/Model.scala
@@ -12,7 +12,12 @@ import mill.api.internal
     colored: Boolean,
     testCp: Seq[os.Path],
     home: os.Path,
-    globSelectors: Seq[String]
+    // globSelectors indicates the strategy for testrunner to find and run test classes
+    // can be either:
+    // - Left(selectors: Seq[String]): - list of glob selectors, testrunner is given a list of glob selectors to run directly
+    // - Right((selectorFolder: os.Path, baseFolder: os.Path)): - a pair of paths, testrunner will try to steal test glob from selectorFolder
+    // and move it actomatically in to baseFolder and run it from there.
+    globSelectors: Either[Seq[String], (os.Path, os.Path)]
 )
 
 @internal object TestArgs {
diff --git a/testrunner/src/mill/testrunner/TestRunnerMain0.scala b/testrunner/src/mill/testrunner/TestRunnerMain0.scala
index a0656cefb6d..ad03f79e689 100644
--- a/testrunner/src/mill/testrunner/TestRunnerMain0.scala
+++ b/testrunner/src/mill/testrunner/TestRunnerMain0.scala
@@ -26,16 +26,28 @@ import mill.util.PrintLogger
       ctx.log.debug(s"Setting ${testArgs.sysProps.size} system properties")
       testArgs.sysProps.foreach { case (k, v) => System.setProperty(k, v) }
 
-      val filter = TestRunnerUtils.globFilter(testArgs.globSelectors)
-
-      val result = TestRunnerUtils.runTestFramework0(
-        frameworkInstances = Framework.framework(testArgs.framework),
-        testClassfilePath = Agg.from(testArgs.testCp),
-        args = testArgs.arguments,
-        classFilter = cls => filter(cls.getName),
-        cl = classLoader,
-        testReporter = DummyTestReporter
-      )(ctx)
+      val result = testArgs.globSelectors match {
+        case Left(selectors) =>
+          val filter = TestRunnerUtils.globFilter(selectors)
+          TestRunnerUtils.runTestFramework0(
+            frameworkInstances = Framework.framework(testArgs.framework),
+            testClassfilePath = Agg.from(testArgs.testCp),
+            args = testArgs.arguments,
+            classFilter = cls => filter(cls.getName),
+            cl = classLoader,
+            testReporter = DummyTestReporter
+          )(ctx)
+        case Right((testClassesFolder, stealFolder)) =>
+          TestRunnerUtils.stealTestFramework0(
+            frameworkInstances = Framework.framework(testArgs.framework),
+            testClassfilePath = Agg.from(testArgs.testCp),
+            args = testArgs.arguments,
+            testClassesFolder = testClassesFolder,
+            stealFolder = stealFolder,
+            cl = classLoader,
+            testReporter = DummyTestReporter
+          )(ctx)
+      }
 
       // Clear interrupted state in case some badly-behaved test suite
       // dirtied the thread-interrupted flag and forgot to clean up. Otherwise,
diff --git a/testrunner/src/mill/testrunner/TestRunnerUtils.scala b/testrunner/src/mill/testrunner/TestRunnerUtils.scala
index 563b1e480c3..1d1049552ae 100644
--- a/testrunner/src/mill/testrunner/TestRunnerUtils.scala
+++ b/testrunner/src/mill/testrunner/TestRunnerUtils.scala
@@ -15,6 +15,8 @@ import scala.jdk.CollectionConverters.IteratorHasAsScala
 
 @internal object TestRunnerUtils {
 
+  private type ClassWithFingerprint = (Class[?], Fingerprint)
+
   def listClassFiles(base: os.Path): geny.Generator[String] = {
     if (os.isDir(base)) {
       os.walk.stream(base).filter(_.ext == "class").map(_.relativeTo(base).toString)
@@ -36,7 +38,7 @@ import scala.jdk.CollectionConverters.IteratorHasAsScala
       cl: ClassLoader,
       framework: Framework,
       classpath: Loose.Agg[os.Path]
-  ): Loose.Agg[(Class[_], Fingerprint)] = {
+  ): Loose.Agg[ClassWithFingerprint] = {
 
     val fingerprints = framework.fingerprints()
 
@@ -45,7 +47,7 @@ import scala.jdk.CollectionConverters.IteratorHasAsScala
       // the tests to run Instead just don't run anything
       .filter(os.exists(_))
       .flatMap { base =>
-        Loose.Agg.from[(Class[_], Fingerprint)](
+        Loose.Agg.from[ClassWithFingerprint](
           listClassFiles(base).map { path =>
             val cls = cl.loadClass(path.stripSuffix(".class").replace('/', '.'))
             val publicConstructorCount =
@@ -85,7 +87,7 @@ import scala.jdk.CollectionConverters.IteratorHasAsScala
       cls: Class[_],
       fingerprints: Array[Fingerprint],
       isModule: Boolean
-  ): Option[(Class[_], Fingerprint)] = {
+  ): Option[ClassWithFingerprint] = {
     fingerprints.find {
       case f: SubclassFingerprint =>
         f.isModule == isModule &&
@@ -129,45 +131,38 @@ import scala.jdk.CollectionConverters.IteratorHasAsScala
     (runner, tasks)
   }
 
-  def runTasks(tasks: Seq[Task], testReporter: TestReporter, runner: Runner)(implicit
-      ctx: Ctx.Log with Ctx.Home
-  ): (String, Iterator[TestResult]) = {
-    val events = new ConcurrentLinkedQueue[Event]()
-    val doneMessage = {
-
-      val taskQueue = tasks.to(mutable.Queue)
-      while (taskQueue.nonEmpty) {
-        val next = taskQueue.dequeue().execute(
-          new EventHandler {
-            def handle(event: Event) = {
-              testReporter.logStart(event)
-              events.add(event)
-              testReporter.logFinish(event)
-            }
-          },
-          Array(new Logger {
-            def debug(msg: String) = ctx.log.outputStream.println(msg)
-            def error(msg: String) = ctx.log.outputStream.println(msg)
-            def ansiCodesSupported() = true
-            def warn(msg: String) = ctx.log.outputStream.println(msg)
-            def trace(t: Throwable) = t.printStackTrace(ctx.log.outputStream)
-            def info(msg: String) = ctx.log.outputStream.println(msg)
-          })
-        )
-
-        taskQueue.enqueueAll(next)
-      }
-      runner.done()
-    }
+  private def executeTasks(
+      tasks: Seq[Task],
+      testReporter: TestReporter,
+      runner: Runner,
+      events: ConcurrentLinkedQueue[Event]
+  )(implicit ctx: Ctx.Log with Ctx.Home): Unit = {
+    val taskQueue = tasks.to(mutable.Queue)
+    while (taskQueue.nonEmpty) {
+      val next = taskQueue.dequeue().execute(
+        new EventHandler {
+          def handle(event: Event) = {
+            testReporter.logStart(event)
+            events.add(event)
+            testReporter.logFinish(event)
+          }
+        },
+        Array(new Logger {
+          def debug(msg: String) = ctx.log.outputStream.println(msg)
+          def error(msg: String) = ctx.log.outputStream.println(msg)
+          def ansiCodesSupported() = true
+          def warn(msg: String) = ctx.log.outputStream.println(msg)
+          def trace(t: Throwable) = t.printStackTrace(ctx.log.outputStream)
+          def info(msg: String) = ctx.log.outputStream.println(msg)
+        })
+      )
 
-    if (doneMessage != null && doneMessage.nonEmpty) {
-      if (doneMessage.endsWith("\n"))
-        ctx.log.outputStream.print(doneMessage)
-      else
-        ctx.log.outputStream.println(doneMessage)
+      taskQueue.enqueueAll(next)
     }
+  }
 
-    val results = for (e <- events.iterator().asScala) yield {
+  def parseRunTaskResults(events: Iterator[Event]): Iterator[TestResult] = {
+    for (e <- events) yield {
       val ex =
         if (e.throwable().isDefined) Some(e.throwable().get) else None
       mill.testrunner.TestResult(
@@ -186,10 +181,35 @@ import scala.jdk.CollectionConverters.IteratorHasAsScala
         ex.map(_.getStackTrace.toIndexedSeq)
       )
     }
+  }
+
+  private def handleRunnerDone(
+      runner: Runner,
+      events: ConcurrentLinkedQueue[Event]
+  ): (String, Iterator[TestResult]) = {
+    val doneMessage = runner.done()
+    if (doneMessage != null && doneMessage.nonEmpty) {
+      if (doneMessage.endsWith("\n"))
+        println(doneMessage.stripSuffix("\n"))
+      else
+        println(doneMessage)
+    }
+
+    val results = parseRunTaskResults(events.iterator().asScala)
 
     (doneMessage, results)
   }
 
+  def runTasks(tasks: Seq[Task], testReporter: TestReporter, runner: Runner)(implicit
+      ctx: Ctx.Log with Ctx.Home
+  ): (String, Iterator[TestResult]) = {
+    // Capture this value outside of the task event handler so it
+    // isn't affected by a test framework's stream redirects
+    val events = new ConcurrentLinkedQueue[Event]()
+    executeTasks(tasks, testReporter, runner, events)
+    handleRunnerDone(runner, events)
+  }
+
   def runTestFramework0(
       frameworkInstances: ClassLoader => Framework,
       testClassfilePath: Loose.Agg[Path],
@@ -208,6 +228,101 @@ import scala.jdk.CollectionConverters.IteratorHasAsScala
     (doneMessage, results.toSeq)
   }
 
+  private def stealTaskFromTestClassesFolder(
+      globSelectorCache: Map[String, ClassWithFingerprint],
+      runner: Runner,
+      stealFolder: os.Path,
+      testClassesFolder: os.Path
+  ): Array[Task] = {
+    // append only log, used to communicate with parent about what test is being stolen
+    // so that the parent can log the stolen test's name to its logger
+    val stealLog = stealFolder / os.up / s"${stealFolder.last}.log"
+    val files = os.list.stream(testClassesFolder).toBuffer
+    while (files.nonEmpty) {
+      val file = files.remove(0)
+      val stolenFile = stealFolder / file.last
+      val stole =
+        try {
+          // we can check for existence of stolenFile first, but it'll require another os call.
+          // it just better to let this call failed in that case.
+          os.move(
+            file,
+            stolenFile,
+            atomicMove = true
+          )
+          true
+        } catch {
+          case e: Exception => false
+        }
+      if (stole) {
+        val selector = stolenFile.last
+        os.write.append(stealLog, s"$selector\n")
+        val taskDefs = globSelectorCache.get(stolenFile.last) match {
+          case Some((cls, fingerprint)) =>
+            Array(new TaskDef(
+              cls.getName.stripSuffix("$"),
+              fingerprint,
+              false,
+              Array(new SuiteSelector)
+            ))
+          case None => Array.empty[TaskDef]
+        }
+        val tasks = runner.tasks(taskDefs)
+        return tasks
+      }
+    }
+
+    Array.empty[Task]
+  }
+
+  def stealTasks(
+      testClasses: Loose.Agg[ClassWithFingerprint],
+      testReporter: TestReporter,
+      runner: Runner,
+      stealFolder: os.Path,
+      testClassesFolder: os.Path
+  )(implicit ctx: Ctx.Log with Ctx.Home): (String, Iterator[TestResult]) = {
+    // Capture this value outside of the task event handler so it
+    // isn't affected by a test framework's stream redirects
+    val events = new ConcurrentLinkedQueue[Event]()
+    val globSelectorCache = testClasses.view.map { case (cls, fingerprint) =>
+      cls.getName.stripSuffix("$") -> (cls, fingerprint)
+    }.toMap
+    while ({
+      val tasks =
+        stealTaskFromTestClassesFolder(globSelectorCache, runner, stealFolder, testClassesFolder)
+      if (tasks.nonEmpty) {
+        executeTasks(tasks, testReporter, runner, events)
+        true
+      } else {
+        false
+      }
+    }) ()
+    handleRunnerDone(runner, events)
+  }
+
+  def stealTestFramework0(
+      frameworkInstances: ClassLoader => Framework,
+      testClassfilePath: Loose.Agg[Path],
+      args: Seq[String],
+      testClassesFolder: os.Path,
+      stealFolder: os.Path,
+      cl: ClassLoader,
+      testReporter: TestReporter
+  )(implicit ctx: Ctx.Log with Ctx.Home): (String, Seq[TestResult]) = {
+
+    val framework = frameworkInstances(cl)
+
+    val runner = framework.runner(args.toArray, Array[String](), cl)
+
+    val testClasses = discoverTests(cl, framework, testClassfilePath)
+
+    val (doneMessage, results) =
+      stealTasks(testClasses, testReporter, runner, stealFolder, testClassesFolder)
+
+    (doneMessage, results.toSeq)
+  }
+
   def getTestTasks0(
       frameworkInstances: ClassLoader => Framework,
       testClassfilePath: Loose.Agg[Path],