Only instantiate tests that we'll run

As we add more variables to the test matrix, assuming the unneeded
ones away becomes too cumbersome.

Author: gzm0

js-envs-test-kit/src/main/scala/org/scalajs/jsenv/test/ComTests.scala

@@ -12,7 +12,7 @@
 
 package org.scalajs.jsenv.test
 
-import org.junit.{Before, Test, AssumptionViolatedException}
+import org.junit.{Test, AssumptionViolatedException}
 import org.junit.Assume._
 
 import org.scalajs.jsenv._
@@ -21,11 +21,6 @@ import org.scalajs.jsenv.test.kit.TestKit
 private[test] class ComTests(config: JSEnvSuiteConfig) {
   private val kit = new TestKit(config.jsEnv, config.awaitTimeout)
 
-  @Before
-  def before: Unit = {
-    assumeTrue("JSEnv needs com support", config.supportsCom)
-  }
-
   @Test
   def basicTest: Unit = {
     kit.withComRun("""

js-envs-test-kit/src/main/scala/org/scalajs/jsenv/test/JSEnvSuite.scala

@@ -67,13 +67,26 @@ private object JSEnvSuiteRunner {
   private def getRunners(config: JSEnvSuiteConfig): java.util.List[Runner] = {
     import java.lang.Boolean.{TRUE, FALSE}
 
-    java.util.Arrays.asList(
-        r[RunTests](config, "withCom" -> FALSE),
-        r[RunTests](config, "withCom" -> TRUE),
-        r[TimeoutRunTests](config, "withCom" -> FALSE),
-        r[TimeoutRunTests](config, "withCom" -> TRUE),
-        r[ComTests](config),
-        r[TimeoutComTests](config)
-    )
+    val runners = new java.util.ArrayList[Runner]
+
+    val withComValues =
+      if (config.supportsCom) List(TRUE, FALSE)
+      else List(FALSE)
+
+    for (withCom <- withComValues)
+      runners.add(r[RunTests](config, "withCom" -> withCom))
+
+    if (config.supportsTimeout) {
+      for (withCom <- withComValues)
+        runners.add(r[TimeoutRunTests](config, "withCom" -> withCom))
+    }
+
+    if (config.supportsCom)
+      runners.add(r[ComTests](config))
+
+    if (config.supportsCom && config.supportsTimeout)
+      runners.add(r[TimeoutComTests](config))
+
+    runners
   }
 }

js-envs-test-kit/src/main/scala/org/scalajs/jsenv/test/RunTests.scala

@@ -19,7 +19,7 @@ import java.nio.file.Files
 import com.google.common.jimfs.Jimfs
 
 import org.junit.Assume._
-import org.junit.{Test, Before, AssumptionViolatedException}
+import org.junit.{Test, AssumptionViolatedException}
 
 import org.scalajs.jsenv._
 import org.scalajs.jsenv.test.kit.{TestKit, Run}

js-envs-test-kit/src/main/scala/org/scalajs/jsenv/test/TimeoutComTests.scala

@@ -14,7 +14,7 @@ package org.scalajs.jsenv.test
 
 import scala.concurrent.duration._
 
-import org.junit.{Before, Test}
+import org.junit.Test
 import org.junit.Assert._
 import org.junit.Assume._
 
@@ -24,12 +24,6 @@ import org.scalajs.jsenv.test.kit.TestKit
 private[test] class TimeoutComTests(config: JSEnvSuiteConfig) {
   private val kit = new TestKit(config.jsEnv, config.awaitTimeout)
 
-  @Before
-  def before: Unit = {
-    assumeTrue("JSEnv needs timeout support", config.supportsTimeout)
-    assumeTrue("JSEnv needs com support", config.supportsCom)
-  }
-
   /** Slack for timeout tests (see #3457)
    *
    *  Empirically we can observe that timing can be off by ~0.1ms. By cutting

js-envs-test-kit/src/main/scala/org/scalajs/jsenv/test/TimeoutRunTests.scala

@@ -14,7 +14,7 @@ package org.scalajs.jsenv.test
 
 import scala.concurrent.duration._
 
-import org.junit.{Before, Test}
+import org.junit.Test
 import org.junit.Assert._
 import org.junit.Assume._
 
@@ -29,11 +29,6 @@ private[test] class TimeoutRunTests(config: JSEnvSuiteConfig, withCom: Boolean)
     else kit.withRun(input)(body)
   }
 
-  @Before
-  def before: Unit = {
-    assumeTrue("JSEnv needs timeout support", config.supportsTimeout)
-  }
-
   /** Slack for timeout tests (see #3457)
    *
    *  Empirically we can observe that timing can be off by ~0.1ms. By cutting