@Test public void findSubtypes() throws Exception {

    assertEquals(new HashSet<Class<?>>(Arrays.asList(Impl1.class, Impl2.class, Impl3.class, Impl4.class)), DescribableModel.findSubtypes(Base.class));
    assertEquals(Collections.singleton(Impl1.class), DescribableModel.findSubtypes(Marker.class));
}