assertEquals(
              EVEN.apply(i) && contents.contains(i),
              filter(createUnfiltered(contents), EVEN).contains(i));
        }
      }
    }

    public void testContainsOnDifferentType() {
      for (List<Integer> contents : SAMPLE_INPUTS) {
        assertFalse(filter(createUnfiltered(contents), EVEN).contains(new Object()));
      }
    }

    public void testAddAllFailsAtomically() {