Add TestModule.discoveredTestClasses target to ease test inspection

scalalib/src/mill/scalalib/TestModule.scala

@@ -3,7 +3,7 @@ package mill.scalalib
 import mill.api.{Ctx, PathRef, Result}
 import mill.define.{Command, Task, TaskModule}
 import mill.scalalib.bsp.{BspBuildTarget, BspModule}
-import mill.testrunner.{Framework, TestArgs, TestResult, TestRunner}
+import mill.testrunner.{Framework, TestArgs, TestResult, TestRunner, TestRunnerUtils}
 import mill.util.Jvm
 import mill.{Agg, T}
 import sbt.testing.Status
@@ -46,6 +46,25 @@ trait TestModule
    */
   def testFramework: T[String]
 
+  def discoveredTestClasses: T[Seq[String]] = T {
+    val classes = Jvm.inprocess(
+      runClasspath().map(_.path),
+      classLoaderOverrideSbtTesting = true,
+      isolated = true,
+      closeContextClassLoaderWhenDone = true,
+      cl => {
+        val framework = Framework.framework(testFramework())(cl)
+        val classes = TestRunnerUtils.discoverTests(cl, framework, testClasspath().map(_.path))
+        classes.toSeq.map(_._1.getName())
+          .map {
+            case s if s.endsWith("$") => s.dropRight(1)
+            case s => s
+          }
+      }
+    )
+    classes.sorted
+  }
+
   /**
    * Discovers and runs the module's tests in a subprocess, reporting the
    * results to the console.

scalalib/test/src/mill/scalalib/TestRunnerTests.scala

@@ -78,17 +78,27 @@ object TestRunnerTests extends TestSuite {
   }
 
   override def tests: Tests = Tests {
-    "TestRunner" - {
-      "utest" - {
-        "test case lookup" - workspaceTest(testrunner) { eval =>
+    test("TestRunner") - {
+      test("utest") - {
+        test("test case lookup") - workspaceTest(testrunner) { eval =>
           val Right((result, _)) = eval.apply(testrunner.utest.test())
           val test = result.asInstanceOf[(String, Seq[mill.testrunner.TestResult])]
           assert(
             test._2.size == 3
           )
           junitReportIn(eval.outPath, "utest").shouldHave(3 -> Status.Success)
         }
-        "testOnly" - {
+        test("discoveredTestClasses") - workspaceTest(testrunner) { eval =>
+          val Right((res, _)) = eval.apply(testrunner.utest.discoveredTestClasses)
+          val expected = Seq(
+            "mill.scalalib.BarTests",
+            "mill.scalalib.FooTests",
+            "mill.scalalib.FoobarTests"
+          )
+          assert(res == expected)
+          expected
+        }
+        test("testOnly") - {
           def testOnly(eval: TestEvaluator, args: Seq[String], size: Int) = {
             val Right((result1, _)) = eval.apply(testrunner.utest.testOnly(args: _*))
             val testOnly = result1.asInstanceOf[(String, Seq[mill.testrunner.TestResult])]
@@ -144,6 +154,12 @@ object TestRunnerTests extends TestSuite {
             junitReportIn(eval.outPath, "scalatest").shouldHave(2 -> Status.Success)
           }
         }
+        test("discoveredTestClasses") - workspaceTest(testrunner) { eval =>
+          val Right((res, _)) = eval.apply(testrunner.scalatest.discoveredTestClasses)
+          val expected = Seq("mill.scalalib.ScalaTestSpec")
+          assert(res == expected)
+          expected
+        }
       }
 
       "ZioTest" - {
@@ -154,6 +170,12 @@ object TestRunnerTests extends TestSuite {
             junitReportIn(eval.outPath, "ziotest").shouldHave(1 -> Status.Success)
           }
         }
+        test("discoveredTestClasses") - workspaceTest(testrunner) { eval =>
+          val Right((res, _)) = eval.apply(testrunner.ziotest.discoveredTestClasses)
+          val expected = Seq("mill.scalalib.ZioTestSpec")
+          assert(res == expected)
+          expected
+        }
       }
     }
   }