[test][windows] Export BAZEL_TEST=1 on windows

This was an oversight from when exporting BAZEL_TEST on Linux.

fixes: #21420

Closes #21444.

PiperOrigin-RevId: 610338496
Change-Id: Icbbdc42b6ea92a2de2b0c558aea47a24493c9d8a

src/test/py/bazel/bazel_windows_test.py

@@ -487,6 +487,40 @@ def testZipUndeclaredTestOutputs(self):
     self.assertTrue(os.path.exists(output_file))
     self.assertFalse(os.path.exists(output_zip))
 
+  def testBazelForwardsRequiredEnvVariable(self):
+    self.CreateWorkspaceWithDefaultRepos('WORKSPACE')
+    self.ScratchFile(
+        'BUILD',
+        [
+            'sh_test(',
+            '  name = "foo_test",',
+            '  srcs = ["foo.sh"],',
+            ')',
+            '',
+        ],
+    )
+    self.ScratchFile(
+        'foo.sh',
+        [
+            """
+            if [[ "$BAZEL_TEST" == "1" ]]; then
+                exit 0
+            else
+                echo "BAZEL_TEST is not set to 1"
+                exit 1
+            fi
+            """,
+        ],
+    )
+
+    exit_code, stdout, stderr = self.RunBazel(
+        [
+            'test',
+            '//:foo_test',
+        ],
+    )
+    self.AssertExitCode(exit_code, 0, stderr, stdout)
+
   def testTestShardStatusFile(self):
     self.CreateWorkspaceWithDefaultRepos('WORKSPACE')
     self.ScratchFile(

tools/test/windows/tw.cc

@@ -628,6 +628,11 @@ bool ExportGtestVariables(const Path& test_tmpdir) {
 }
 
 bool ExportMiscEnvvars(const Path& cwd) {
+  // Add BAZEL_TEST environment variable.
+  if (!SetEnv(L"BAZEL_TEST", L"1")) {
+    return false;
+  }
+
   for (const wchar_t* name :
        {L"TEST_INFRASTRUCTURE_FAILURE_FILE", L"TEST_LOGSPLITTER_OUTPUT_FILE",
         L"TEST_PREMATURE_EXIT_FILE", L"TEST_UNUSED_RUNFILES_LOG_FILE",