filtered.clear();
    assertEquals(ImmutableMap.of("one", 1, "three", 3), unfiltered);
    assertTrue(filtered.isEmpty());
  }

  public void testFilteredEntriesIllegalPut() {
    Map<String, Integer> unfiltered = createUnfiltered();
    unfiltered.put("cat", 3);
    unfiltered.put("dog", 2);
    unfiltered.put("horse", 5);