Set<String> unfiltered = Sets.newLinkedHashSet();
                unfiltered.add("yyy");
                Collections.addAll(unfiltered, elements);
                unfiltered.add("zzz");
                return Sets.filter(unfiltered, Collections2Test.NOT_YYY_ZZZ);
              }
            })
        .named("Sets.filter")
        .withFeatures(

    suite.addTest(testsForFilterFiltered());
    suite.addTest(testsForTransform());
    suite.addTestSuite(Collections2Test.class);
    return suite;
  }

  static final Predicate<@Nullable String> NOT_YYY_ZZZ =
      input -> !"yyy".equals(input) && !"zzz".equals(input);

  static final Predicate<String> LENGTH_1 = input -> input.length() == 1;

  @J2ktIncompatible
  @GwtIncompatible // suite
  private static Test testsForFilter() {

    suite.addTest(testsForFilterFiltered());
    suite.addTest(testsForTransform());
    suite.addTestSuite(Collections2Test.class);
    return suite;
  }

  static final Predicate<@Nullable String> NOT_YYY_ZZZ =
      input -> !"yyy".equals(input) && !"zzz".equals(input);

  static final Predicate<String> LENGTH_1 = input -> input.length() == 1;

  @J2ktIncompatible
  @GwtIncompatible // suite
  private static Test testsForFilter() {

    Map<String, Integer> filtered = Maps.filterKeys(unfiltered, NOT_LENGTH_3);
    filtered.put("a", 1);
    filtered.put("b", 2);
    assertEquals(ImmutableMap.of("a", 1, "b", 2), filtered);

    try {
      filtered.put("yyy", 3);
      fail();
    } catch (IllegalArgumentException expected) {
    }
  }

  public void testFilteredKeysIllegalPutAll() {
    Map<String, Integer> unfiltered = createUnfiltered();

    Map<String, Integer> filtered = Maps.filterKeys(unfiltered, NOT_LENGTH_3);
    filtered.put("a", 1);
    filtered.put("b", 2);
    assertEquals(ImmutableMap.of("a", 1, "b", 2), filtered);

    try {
      filtered.put("yyy", 3);
      fail();
    } catch (IllegalArgumentException expected) {
    }
  }

  public void testFilteredKeysIllegalPutAll() {
    Map<String, Integer> unfiltered = createUnfiltered();

                Set<String> unfiltered = Sets.newLinkedHashSet();
                unfiltered.add("yyy");
                Collections.addAll(unfiltered, elements);
                unfiltered.add("zzz");
                return Sets.filter(unfiltered, Collections2Test.NOT_YYY_ZZZ);
              }
            })
        .named("Sets.filter")
        .withFeatures(