Simplified test helper code

This also avoids defining a `T.command` inside of a class which does not extend `mill.define.Module`.

build.sc

@@ -175,42 +175,42 @@ object `native-mostly-static` extends ScalaJsCliMostlyStaticNativeImage
 object tests extends ScalaModule {
   def scalaVersion = scala213
 
-  object test extends ScalaTests {
+  object test extends ScalaTests with TestModule.Munit {
     def ivyDeps = super.ivyDeps() ++ Seq(
       ivy"org.scalameta::munit:0.7.29",
       ivy"com.lihaoyi::os-lib:0.9.1",
       ivy"com.lihaoyi::pprint:0.8.1"
     )
-    def testFramework = "munit.Framework"
-
-    private final class TestHelper(
-      launcherTask: T[PathRef]
-    ) {
-      def test(args: String*) = {
-        val argsTask = T.task {
-          val launcher = launcherTask().path
-          val extraArgs = Seq(
-            s"-Dtest.scala-js-cli.path=$launcher",
-            s"-Dtest.scala-js-cli.scala-js-version=$scalaJsVersion"
-          )
-          args ++ extraArgs
-        }
-        T.command {
-          testTask(argsTask, T.task(Seq.empty[String]))()
-        }
+
+    def testHelper(
+      launcherTask: Task[PathRef],
+      args: Seq[String]
+    ): Task[(String, Seq[mill.testrunner.TestResult])] = {
+      val argsTask = T.task {
+        val launcher = launcherTask().path
+        val extraArgs = Seq(
+          s"-Dtest.scala-js-cli.path=$launcher",
+          s"-Dtest.scala-js-cli.scala-js-version=$scalaJsVersion"
+        )
+        args ++ extraArgs
       }
+      testTask(argsTask, T.task(Seq.empty[String]))
     }
 
-    def test(args: String*) =
-      jvm(args: _*)
-    def jvm(args: String*) =
-      new TestHelper(cli.standaloneLauncher).test(args: _*)
-    def native(args: String*) =
-      new TestHelper(native0.nativeImage).test(args: _*)
-    def nativeStatic(args: String*) =
-      new TestHelper(`native-static`.nativeImage).test(args: _*)
-    def nativeMostlyStatic(args: String*) =
-      new TestHelper(`native-mostly-static`.nativeImage).test(args: _*)
+    override def test(args: String*) = jvm(args: _*)
+
+    def jvm(args: String*): Command[(String, Seq[mill.testrunner.TestResult])] = T.command {
+      testHelper(cli.standaloneLauncher, args)
+    }
+    def native(args: String*) = T.command {
+      testHelper(native0.nativeImage, args)
+    }
+    def nativeStatic(args: String*) = T.command {
+      testHelper(`native-static`.nativeImage, args)
+    }
+    def nativeMostlyStatic(args: String*) = T.command {
+      testHelper(`native-mostly-static`.nativeImage, args)
+    }
   }
 }