Partially revert 670cbb9a

... but continue to execute `Abstract*Tests` classes.

build.gradle

@@ -317,12 +317,16 @@ configure([rootProject] + javaProjects) { project ->
 	}
 
 	test {
-		useJUnitPlatform()
-		scanForTestClasses = false
-		include(["**/*Tests.class", "**/*Test.class"])
 		systemProperty("java.awt.headless", "true")
 		systemProperty("testGroups", project.properties.get("testGroups"))
 		systemProperty("io.netty.leakDetection.level", "paranoid")
+		useJUnitPlatform()
+		scanForTestClasses = false
+		include(["**/*Tests.class", "**/*Test.class"])
+		// Since we set scanForTestClasses to false, we need to filter out inner
+		// classes with the "$" pattern; otherwise, using -Dtest.single=MyTests to
+		// run MyTests by itself will fail if MyTests contains any inner classes.
+		exclude(['**/*$*'])
 	}
 
 	checkstyle {