@Test
  public void testAddFilter() throws Exception {
    final DebugChecker checker = new DebugChecker();
    final DebugFilter filter = new DebugFilter();

    checker.addFilter(filter);

    filter.resetFilter();
    final SortedSet<LocalizedMessage> messages = Sets.newTreeSet();
    messages.add(
        new LocalizedMessage(
            0, 0, "a Bundle", "message.key", new Object[] {"arg"}, null, getClass(), null));
    checker.fireErrors("Some File Name", messages);
    assertTrue("Checker.fireErrors() doesn't call filter", filter.wasCalled());
  }