@Test
 public void dontFailWithoutParentForGetThreadGroup() {
   managerWithoutOriginal.getThreadGroup();
 }
 @Test
 public void provideThreadGroupOfOriginalSecurityManager() {
   ThreadGroup threadGroup = new ThreadGroup("dummy name");
   when(originalSecurityManager.getThreadGroup()).thenReturn(threadGroup);
   assertThat(managerWithOriginal.getThreadGroup(), is(threadGroup));
 }