Filter out anonymous classes during test discovery

kotlinlib/test/resources/hello-world-kotlin/main/kotest/src/FooTest.kt

@@ -0,0 +1,15 @@
+package hello.tests
+
+import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.shouldBe
+import hello.getHelloString
+
+class FooTest : FunSpec({
+    test("testFailure") {
+        getHelloString() shouldBe "Hello, world!"
+    }
+
+    test("testSuccess") {
+        getHelloString() shouldBe "WRONG!"
+    }
+})

kotlinlib/test/src/mill/kotlinlib/HelloWorldTests.scala

@@ -24,6 +24,11 @@ object HelloWorldTests extends TestSuite {
           ivy"org.jetbrains.kotlin:kotlin-test-junit:${this.kotlinVersion()}"
         )
       }
+      object kotest extends KotlinTests with TestModule.Junit5 {
+        override def ivyDeps = super.ivyDeps() ++ Agg(
+          ivy"io.kotest:kotest-runner-junit5-jvm:5.9.1"
+        )
+      }
     }
     object main extends Cross[MainCross](kotlinVersions)
   }
@@ -68,6 +73,23 @@ object HelloWorldTests extends TestSuite {
         )
       })
     }
+    test("kotest") {
+      val eval = testEval()
+
+      HelloWorldKotlin.main.crossModules.foreach(m => {
+        val Right(discovered) = eval.apply(m.kotest.discoveredTestClasses)
+        assert(discovered.value == Seq("hello.tests.FooTest"))
+
+        val Left(Result.Failure(_, Some(v1))) = eval.apply(m.kotest.test())
+
+        assert(
+          v1._2(0).fullyQualifiedName == "hello.tests.FooTest",
+          v1._2(0).status == "Success",
+          v1._2(1).fullyQualifiedName == "hello.tests.FooTest",
+          v1._2(1).status == "Failure"
+        )
+      })
+    }
     test("failures") {
       val eval = testEval()
 

testrunner/src/mill/testrunner/TestRunnerUtils.scala

@@ -70,6 +70,12 @@ import scala.jdk.CollectionConverters.IteratorHasAsScala
             .flatten
         )
       }
+      // I think this is a bug in sbt-junit-interface. AFAICT, JUnit is not
+      // meant to pick up non-static inner classes as test suites, and doing
+      // so makes the jimfs test suite fail
+      //
+      // https://stackoverflow.com/a/17468590
+      .filter { case (c, f) => !c.isMemberClass && !c.isAnonymousClass }
 
     testClasses
   }
@@ -109,12 +115,6 @@ import scala.jdk.CollectionConverters.IteratorHasAsScala
 
     val runner = framework.runner(args.toArray, Array[String](), cl)
     val testClasses = discoverTests(cl, framework, testClassfilePath)
-      // I think this is a bug in sbt-junit-interface. AFAICT, JUnit is not
-      // meant to pick up non-static inner classes as test suites, and doing
-      // so makes the jimfs test suite fail
-      //
-      // https://stackoverflow.com/a/17468590
-      .filter { case (c, f) => !c.isMemberClass }
 
     val tasks = runner.tasks(
       for ((cls, fingerprint) <- testClasses.iterator.toArray if classFilter(cls))