@Test
 public void testAddRemoveListener() {
   ResourceManager resourceManagerX = new ResourceManager();
   IResourceListener listener = new MockResourceListener();
   Assert.assertTrue(resourceManagerX.addResourceListener(listener));
   Assert.assertFalse(resourceManagerX.addResourceListener(listener)); // Add again
   Assert.assertTrue(resourceManagerX.removeResourceListener(listener));
   Assert.assertFalse(resourceManagerX.removeResourceListener(listener)); // Add again
 }