java.util.ServiceLoader.load() function is useless and only returns empty result

I'm trying to use Java ServiceLoader in Scala 2.10 to find all my test classes by reflection:

  val services = ServiceLoader.load(classOf[MyClass])
  for (service <- services.asScala) {
    test(service.getClass.getCanonicalName) {
      println(service)
      ... test code
    }
  }

I'm very sure 'MyClass' has several subclasses which contains test cases, as I can use 'classOf[]' function to find them in the same code snippet

However, my test always ends with

Empty test suite.

Is the ServiceLoader not working in Scala? How to fix or circumvent this problem?