@Test
  public void testRemoveService() {
    ServiceHolder tested = new ServiceHolder();
    Object service = new Object();

    // Get the hash set.
    Set<Object> servicesSet = getField(tested, Set.class);
    servicesSet.add(service);

    tested.removeService(service);

    assertTrue("Set should be empty after removeal.", servicesSet.isEmpty());
  }
  @Test
  public void testAddService() {
    ServiceHolder tested = new ServiceHolder();
    Object service = new Object();

    tested.addService(service);

    Set<String> services = getField(tested, "services");

    assertEquals("Size of the \"services\" Set should be 1", 1, services.size());
    assertSame(
        "The services Set should didn't contain the expect service",
        service,
        services.iterator().next());
  }