Fix scalameta#497 - don't load fixtures for empty test suites

Previously, MUnit loaded fixtures even for test suites that had no
tests. Now, we skip the entire suite if there are no tests to run.

munit/shared/src/main/scala/munit/MUnitRunner.scala

@@ -174,7 +174,7 @@ class MUnitRunner(val cls: Class[_ <: Suite], newInstance: () => Suite)
   }
 
   private def runAll(notifier: RunNotifier): Future[Unit] = {
-    if (PlatformCompat.isIgnoreSuite(cls)) {
+    if (PlatformCompat.isIgnoreSuite(cls) || munitTests.isEmpty) {
       val description = getDescription()
       notifier.fireTestIgnored(description)
       return Future.successful(())

tests/shared/src/main/scala/munit/Issue497FrameworkSuite.scala

@@ -0,0 +1,44 @@
+package munit
+
+import org.junit.experimental.categories.Category
+
+class Slow extends Tag("Slow")
+
+@Category(Array(classOf[Slow]))
+class Issue497FrameworkSuite extends FunSuite {
+  def println(msg: String): Unit = TestingConsole.out.println(msg)
+  val myFixture = new Fixture[Unit]("myFixture") {
+    def apply(): Unit = println("### myFixture apply() ###")
+
+    override def beforeAll(): Unit = {
+      println("### beforeAll is running ###")
+    }
+
+    override def afterAll(): Unit = {
+      println("### afterAll is running ###")
+    }
+  }
+  override def munitFixtures = List(myFixture)
+
+  test("test1") {
+    myFixture()
+    assertEquals(1, 1)
+  }
+
+  test("test2") {
+    myFixture()
+    assertEquals(1, 1)
+  }
+}
+
+object Issue497FrameworkSuite
+    extends FrameworkTest(
+      classOf[Issue497FrameworkSuite],
+      """|munit.Issue497FrameworkSuite:
+         |""".stripMargin,
+      arguments = Array("--exclude-categories=munit.Slow"),
+      tags = Set(
+        OnlyJVM
+      ),
+      format = StdoutFormat
+    )

tests/shared/src/test/scala/munit/FrameworkSuite.scala

@@ -29,6 +29,7 @@ class FrameworkSuite extends BaseFrameworkSuite {
     AssertionsFrameworkSuite,
     Issue179FrameworkSuite,
     Issue285FrameworkSuite,
+    Issue497FrameworkSuite,
     ScalaCheckExceptionFrameworkSuite,
     BoxedFrameworkSuite
   )