diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 43feeebfd74f..56b0b7457f83 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -119,9 +119,9 @@ jobs:
         run: sbt ";dotty-bootstrapped/compile ;dotty-bootstrapped/test"
         shell: cmd
 
-      # - name: Scala.js Test
-      #   run: sbt ";sjsJUnitTests/test"
-      #   shell: cmd
+      - name: Scala.js Test
+        run: sbt ";sjsJUnitTests/test ;sjsCompilerTests/test"
+        shell: cmd
 
   community_build:
     runs-on: [self-hosted, Linux]
diff --git a/compiler/test/dotty/tools/dotc/BootstrappedOnlyCompilationTests.scala b/compiler/test/dotty/tools/dotc/BootstrappedOnlyCompilationTests.scala
index 8682218f9fe2..74ae28909893 100644
--- a/compiler/test/dotty/tools/dotc/BootstrappedOnlyCompilationTests.scala
+++ b/compiler/test/dotty/tools/dotc/BootstrappedOnlyCompilationTests.scala
@@ -22,7 +22,7 @@ class BootstrappedOnlyCompilationTests extends ParallelTesting {
   // Test suite configuration --------------------------------------------------
 
   def maxDuration = 60.seconds
-  def numberOfSlaves = 5
+  def numberOfSlaves = Runtime.getRuntime().availableProcessors()
   def safeMode = Properties.testsSafeMode
   def isInteractive = SummaryReport.isInteractive
   def testFilter = Properties.testsFilter
@@ -30,7 +30,7 @@ class BootstrappedOnlyCompilationTests extends ParallelTesting {
 
   // Positive tests ------------------------------------------------------------
 
-  @Test def posMacros: Unit = if (!scala.util.Properties.isWin) {
+  @Test def posMacros: Unit = {
     implicit val testGroup: TestGroup = TestGroup("compilePosMacros")
     aggregateTests(
       compileFilesInDir("tests/bench", defaultOptions),
@@ -129,17 +129,20 @@ class BootstrappedOnlyCompilationTests extends ParallelTesting {
     )
   }.checkRuns()
 
-  @Test def runWithCompiler: Unit = if (!scala.util.Properties.isWin) {
+  @Test def runWithCompiler: Unit = {
     implicit val testGroup: TestGroup = TestGroup("runWithCompiler")
-    aggregateTests(
+    val basicTests = List(
       compileFilesInDir("tests/run-with-compiler", withCompilerOptions),
       compileFilesInDir("tests/run-staging", withStagingOptions),
-      compileFilesInDir("tests/run-custom-args/tasty-inspector", withTastyInspectorOptions),
-      compileDir("tests/run-custom-args/tasty-interpreter", withTastyInspectorOptions),
-    ).checkRuns()
+      compileFilesInDir("tests/run-custom-args/tasty-inspector", withTastyInspectorOptions)
+    )
+    val tests =
+      if (scala.util.Properties.isWin) basicTests
+      else compileDir("tests/run-custom-args/tasty-interpreter", withTastyInspectorOptions) :: basicTests
+    aggregateTests(tests: _*).checkRuns()
   }
 
-  @Test def runBootstrappedOnly: Unit = if (!scala.util.Properties.isWin) {
+  @Test def runBootstrappedOnly: Unit = {
     implicit val testGroup: TestGroup = TestGroup("runBootstrappedOnly")
     aggregateTests(
       compileFilesInDir("tests/run-bootstrapped", withCompilerOptions),
@@ -151,7 +154,7 @@ class BootstrappedOnlyCompilationTests extends ParallelTesting {
   // Pickling tests are very memory intensive and as such need to be run with a
   // lower level of concurrency as to not kill their running VMs
 
-  @Test def picklingWithCompiler: Unit = if (!scala.util.Properties.isWin) {
+  @Test def picklingWithCompiler: Unit = {
     val jvmBackendFilter = FileFilter.exclude(List("BTypes.scala", "Primitives.scala")) // TODO
     implicit val testGroup: TestGroup = TestGroup("testPicklingWithCompiler")
     aggregateTests(
diff --git a/compiler/test/dotty/tools/dotc/CompilationTests.scala b/compiler/test/dotty/tools/dotc/CompilationTests.scala
index 036b97dd3581..ed50b23e9c68 100644
--- a/compiler/test/dotty/tools/dotc/CompilationTests.scala
+++ b/compiler/test/dotty/tools/dotc/CompilationTests.scala
@@ -16,21 +16,12 @@ import scala.concurrent.duration._
 import TestSources.sources
 import vulpix._
 
-class CompilationTests extends ParallelTesting {
+class CompilationTests {
   import ParallelTesting._
   import TestConfiguration._
   import CompilationTests._
   import CompilationTest.aggregateTests
 
-  // Test suite configuration --------------------------------------------------
-
-  def maxDuration = 45.seconds
-  def numberOfSlaves = 5
-  def safeMode = Properties.testsSafeMode
-  def isInteractive = SummaryReport.isInteractive
-  def testFilter = Properties.testsFilter
-  def updateCheckFiles: Boolean = Properties.testsUpdateCheckfile
-
   // Positive tests ------------------------------------------------------------
 
   @Test def pos: Unit = {
@@ -333,7 +324,19 @@ class CompilationTests extends ParallelTesting {
 
 }
 
-object CompilationTests {
+object CompilationTests extends ParallelTesting {
+  // Test suite configuration --------------------------------------------------
+
+  def maxDuration = 45.seconds
+  def numberOfSlaves = Runtime.getRuntime().availableProcessors()
+  def safeMode = Properties.testsSafeMode
+  def isInteractive = SummaryReport.isInteractive
+  def testFilter = Properties.testsFilter
+  def updateCheckFiles: Boolean = Properties.testsUpdateCheckfile
+
   implicit val summaryReport: SummaryReporting = new SummaryReport
-  @AfterClass def cleanup(): Unit = summaryReport.echoSummary()
+  @AfterClass def tearDown(): Unit = {
+    super.cleanup()
+    summaryReport.echoSummary()
+  }
 }
diff --git a/compiler/test/dotty/tools/dotc/FromTastyTests.scala b/compiler/test/dotty/tools/dotc/FromTastyTests.scala
index 151d0826a176..4fa7dd016cd8 100644
--- a/compiler/test/dotty/tools/dotc/FromTastyTests.scala
+++ b/compiler/test/dotty/tools/dotc/FromTastyTests.scala
@@ -9,19 +9,10 @@ import java.io.{File => JFile}
 
 import scala.concurrent.duration._
 
-class FromTastyTests extends ParallelTesting {
+class FromTastyTests {
   import TestConfiguration._
   import FromTastyTests._
 
-  // Test suite configuration --------------------------------------------------
-
-  def maxDuration = 30.seconds
-  def numberOfSlaves = 5
-  def safeMode = Properties.testsSafeMode
-  def isInteractive = SummaryReport.isInteractive
-  def testFilter = Properties.testsFilter
-  def updateCheckFiles: Boolean = Properties.testsUpdateCheckfile
-
   @Test def posTestFromTasty: Unit = {
     // Can be reproduced with
     // > sbt
@@ -46,7 +37,19 @@ class FromTastyTests extends ParallelTesting {
   }
 }
 
-object FromTastyTests {
+object FromTastyTests extends ParallelTesting {
+  // Test suite configuration --------------------------------------------------
+
+  def maxDuration = 30.seconds
+  def numberOfSlaves = Runtime.getRuntime().availableProcessors()
+  def safeMode = Properties.testsSafeMode
+  def isInteractive = SummaryReport.isInteractive
+  def testFilter = Properties.testsFilter
+  def updateCheckFiles: Boolean = Properties.testsUpdateCheckfile
+
   implicit val summaryReport: SummaryReporting = new SummaryReport
-  @AfterClass def cleanup(): Unit = summaryReport.echoSummary()
+  @AfterClass def tearDown(): Unit = {
+    super.cleanup()
+    summaryReport.echoSummary()
+  }
 }
diff --git a/compiler/test/dotty/tools/dotc/IdempotencyTests.scala b/compiler/test/dotty/tools/dotc/IdempotencyTests.scala
index 1d8b353152ef..30dbb47475ff 100644
--- a/compiler/test/dotty/tools/dotc/IdempotencyTests.scala
+++ b/compiler/test/dotty/tools/dotc/IdempotencyTests.scala
@@ -13,20 +13,11 @@ import scala.concurrent.duration._
 import vulpix._
 
 
-class IdempotencyTests extends ParallelTesting {
+class IdempotencyTests {
   import TestConfiguration._
   import IdempotencyTests._
   import CompilationTest.aggregateTests
 
-  // Test suite configuration --------------------------------------------------
-
-  def maxDuration = 30.seconds
-  def numberOfSlaves = 5
-  def safeMode = Properties.testsSafeMode
-  def isInteractive = SummaryReport.isInteractive
-  def testFilter = Properties.testsFilter
-  def updateCheckFiles: Boolean = Properties.testsUpdateCheckfile
-
   @Category(Array(classOf[SlowTests]))
   @Test def idempotency: Unit = {
     implicit val testGroup: TestGroup = TestGroup("idempotency")
@@ -71,7 +62,19 @@ class IdempotencyTests extends ParallelTesting {
 
 }
 
-object IdempotencyTests {
+object IdempotencyTests extends ParallelTesting {
+  // Test suite configuration --------------------------------------------------
+
+  def maxDuration = 30.seconds
+  def numberOfSlaves = 5
+  def safeMode = Properties.testsSafeMode
+  def isInteractive = SummaryReport.isInteractive
+  def testFilter = Properties.testsFilter
+  def updateCheckFiles: Boolean = Properties.testsUpdateCheckfile
+
   implicit val summaryReport: SummaryReporting = new SummaryReport
-  @AfterClass def cleanup(): Unit = summaryReport.echoSummary()
+  @AfterClass def tearDown(): Unit = {
+    super.cleanup()
+    summaryReport.echoSummary()
+  }
 }
diff --git a/compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala b/compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala
index 4fd415a1dcd2..c6be1856564a 100644
--- a/compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala
+++ b/compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala
@@ -49,6 +49,9 @@ trait RunnerOrchestration {
   def runMain(classPath: String)(implicit summaryReport: SummaryReporting): Status =
     monitor.runMain(classPath)
 
+  /** Kill all processes */
+  def cleanup() = monitor.killAll()
+
   private val monitor = new RunnerMonitor
 
   /** The runner monitor object keeps track of child JVM processes by keeping
@@ -167,14 +170,15 @@ trait RunnerOrchestration {
         .start()
     }
 
-    private val allRunners = List.fill(numberOfSlaves)(new Runner(createProcess))
-    private val freeRunners = mutable.Queue(allRunners: _*)
+    private val freeRunners = mutable.Queue.empty[Runner]
     private val busyRunners = mutable.Set.empty[Runner]
 
     private def getRunner(): Runner = synchronized {
-      while (freeRunners.isEmpty) wait()
+      while (freeRunners.isEmpty && busyRunners.size >= numberOfSlaves) wait()
 
-      val runner = freeRunners.dequeue()
+      val runner =
+        if (freeRunners.isEmpty) new Runner(createProcess)
+        else freeRunners.dequeue()
       busyRunners += runner
 
       notify()
@@ -194,7 +198,10 @@ trait RunnerOrchestration {
       result
     }
 
-    private def killAll(): Unit = allRunners.foreach(_.kill())
+    def killAll(): Unit = {
+      freeRunners.foreach(_.kill())
+      busyRunners.foreach(_.kill())
+    }
 
     // On shutdown, we need to kill all runners:
     sys.addShutdownHook(killAll())
diff --git a/compiler/test/dotty/tools/vulpix/VulpixMetaTests.scala b/compiler/test/dotty/tools/vulpix/VulpixMetaTests.scala
index e79b983c2b83..befb4701f371 100644
--- a/compiler/test/dotty/tools/vulpix/VulpixMetaTests.scala
+++ b/compiler/test/dotty/tools/vulpix/VulpixMetaTests.scala
@@ -1,7 +1,7 @@
 package dotty.tools
 package vulpix
 
-import org.junit.Test
+import org.junit.{ Test, AfterClass }
 import org.junit.experimental.categories.Category
 import scala.concurrent.duration._
 import TestConfiguration._
@@ -11,14 +11,8 @@ import TestConfiguration._
  *  output against an expected result.
  */
 @Category(Array(classOf[dotty.VulpixMetaTests]))
-class VulpixMetaTests extends ParallelTesting {
-  def maxDuration = 1.seconds
-  // Ensure maximum reproducibility.
-  def numberOfSlaves = 1
-  def safeMode = false // Don't fork a new VM after each run test
-  def isInteractive = false // Don't beautify output for interactive use.
-  def testFilter = None // Run all the tests.
-  def updateCheckFiles: Boolean = false
+class VulpixMetaTests {
+  import VulpixMetaTests._
 
   implicit val summaryReport: SummaryReporting = new SummaryReport
   implicit def testGroup: TestGroup = TestGroup("VulpixMetaTests")
@@ -27,3 +21,16 @@ class VulpixMetaTests extends ParallelTesting {
   @Test def compileNeg: Unit = compileFilesInDir("tests/vulpix-tests/meta/neg", defaultOptions).checkExpectedErrors()
   @Test def runAll: Unit     = compileFilesInDir("tests/vulpix-tests/meta/run", defaultOptions).checkRuns()
 }
+
+object VulpixMetaTests extends ParallelTesting {
+  def maxDuration = 1.seconds
+  // Ensure maximum reproducibility.
+  def numberOfSlaves = 1
+  def safeMode = false // Don't fork a new VM after each run test
+  def isInteractive = false // Don't beautify output for interactive use.
+  def testFilter = None // Run all the tests.
+  def updateCheckFiles: Boolean = false
+
+  @AfterClass
+  def tearDown() = this.cleanup()
+}
\ No newline at end of file
diff --git a/compiler/test/dotty/tools/vulpix/VulpixUnitTests.scala b/compiler/test/dotty/tools/vulpix/VulpixUnitTests.scala
index a813138fedba..cdbd55af61d4 100644
--- a/compiler/test/dotty/tools/vulpix/VulpixUnitTests.scala
+++ b/compiler/test/dotty/tools/vulpix/VulpixUnitTests.scala
@@ -3,30 +3,24 @@ package vulpix
 
 import java.io.{File => JFile}
 import org.junit.Assert._
-import org.junit.Test
+import org.junit.{ Test, AfterClass }
 
 import scala.concurrent.duration._
 import scala.util.control.NonFatal
 
 /** Unit tests for the Vulpix test suite */
-class VulpixUnitTests extends ParallelTesting {
+class VulpixUnitTests {
+  import VulpixUnitTests._
   import TestConfiguration._
 
   implicit val _: SummaryReporting = new NoSummaryReport
 
   implicit def testGroup: TestGroup = TestGroup("VulpixTests")
 
-  def maxDuration = 3.seconds
-  def numberOfSlaves = 5
-  def safeMode = sys.env.get("SAFEMODE").isDefined
-  def isInteractive = !sys.env.contains("DRONE")
-  def testFilter = None
-  def updateCheckFiles: Boolean = false
-
   // To fail with something else than an AssertionError
   def fail(): Unit = throw new Exception("didn't fail properly")
 
-  @Test def missingFile: Unit = if (!scala.util.Properties.isWin)
+  @Test def missingFile: Unit =
     try {
       compileFile("tests/vulpix-tests/unit/i-dont-exist.scala", defaultOptions).expectFailure.checkExpectedErrors()
       fail()
@@ -64,7 +58,7 @@ class VulpixUnitTests extends ParallelTesting {
   @Test def runDiffOutput1: Unit =
     compileFile("tests/vulpix-tests/unit/runDiffOutput1.scala", defaultOptions).expectFailure.checkRuns()
 
-  @Test def runStackOverflow: Unit = if (!scala.util.Properties.isWin)
+  @Test def runStackOverflow: Unit =
     compileFile("tests/vulpix-tests/unit/stackOverflow.scala", defaultOptions).expectFailure.checkRuns()
 
   @Test def runOutRedirects: Unit =
@@ -82,7 +76,7 @@ class VulpixUnitTests extends ParallelTesting {
   @Test def deadlock: Unit =
     compileFile("tests/vulpix-tests/unit/deadlock.scala", defaultOptions).expectFailure.checkRuns()
 
-  @Test def badJava: Unit = if (!scala.util.Properties.isWin)
+  @Test def badJava: Unit =
     try {
       compileFile("tests/vulpix-tests/unit/BadJava.java", defaultOptions).suppressAllOutput.checkCompile()
       fail()
@@ -90,7 +84,7 @@ class VulpixUnitTests extends ParallelTesting {
       case ae: AssertionError => assertTrue(ae.getMessage.contains("java compilation failed"))
     }
 
-  @Test def runTimeout: Unit = if (!scala.util.Properties.isWin) {
+  @Test def runTimeout: Unit = {
     val fileName = s"tests/vulpix-tests/unit/timeout.scala"
     try {
       compileFile(fileName, defaultOptions).checkRuns()
@@ -103,3 +97,16 @@ class VulpixUnitTests extends ParallelTesting {
     }
   }
 }
+
+
+object VulpixUnitTests extends ParallelTesting {
+  def maxDuration = 3.seconds
+  def numberOfSlaves = 5
+  def safeMode = sys.env.get("SAFEMODE").isDefined
+  def isInteractive = !sys.env.contains("DRONE")
+  def testFilter = None
+  def updateCheckFiles: Boolean = false
+
+  @AfterClass
+  def tearDown() = this.cleanup()
+}
\ No newline at end of file