new IteratorTester<E>(
        4,
        MODIFIABLE,
        getSubjectGenerator().order(asList(e0(), e1(), e1(), e2())),
        IteratorTester.KnownOrder.KNOWN_ORDER) {
      @Override
      protected Iterator<E> newTargetIterator() {
        return getSubjectGenerator().create(e0(), e1(), e1(), e2()).iterator();
      }
    }.test();
  }

  @CollectionFeature.Require(value = SUPPORTS_ITERATOR_REMOVE, absent = KNOWN_ORDER)

    new IteratorTester<E>(
        4,
        MODIFIABLE,
        getSubjectGenerator().order(asList(e0(), e1(), e1(), e2())),
        IteratorTester.KnownOrder.KNOWN_ORDER) {
      @Override
      protected Iterator<E> newTargetIterator() {
        return getSubjectGenerator().create(e0(), e1(), e1(), e2()).iterator();
      }
    }.test();
  }

  @CollectionFeature.Require(value = SUPPORTS_ITERATOR_REMOVE, absent = KNOWN_ORDER)

        int depth1 = e1.getDepth();
        int depth2 = e2.getDepth();

        if (depth1 == depth2) {
            ArtifactVersion v1 = new DefaultArtifactVersion(e1.getVersion());
            ArtifactVersion v2 = new DefaultArtifactVersion(e2.getVersion());

            if (newerFirst) {
                return v1.compareTo(v2) > 0 ? e1 : e2;
            }

        assertNotNull(collector.getProblems());
        assertEquals(0, collector.getProblems().size());

        collector.add(null, "MESSAGE1", -1, -1, null);

        Exception e2 = new Exception();
        collector.add(Severity.WARNING, null, 42, 127, e2);

        assertEquals(2, collector.getProblems().size());

        Problem p1 = collector.getProblems().get(0);
        assertEquals(Severity.ERROR, p1.getSeverity());

        "containsDuplicates.retainAll(subset) should return true",
        collection.retainAll(MinimalCollection.of(e2())));
    expectContents(e2());
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(SEVERAL)
  public void testRetainAll_countIgnored() {
    resetContainer(getSubjectGenerator().create(e0(), e2(), e1(), e0()));
    assertTrue(getList().retainAll(asList(e0(), e1())));

  // TODO: rename e3, e4 => missing1, missing2
  private final E e0;
  private final E e1;
  private final E e2;
  private final E e3;
  private final E e4;

  public SampleElements(E e0, E e1, E e2, E e3, E e4) {
    this.e0 = e0;
    this.e1 = e1;
    this.e2 = e2;
    this.e3 = e3;
    this.e4 = e4;
  }

  @Override
  public Iterator<E> iterator() {
    return asList().iterator();
  }

                Arrays.sort(sortedExits, (e1, e2) -> {
                    if (e1.getDepth() == e2.getDepth()) {
                        if (e2.getPomOrder() == e1.getPomOrder()) {
                            return e1.getTarget()
                                    .toString()
                                    .compareTo(e2.getTarget().toString());
                        }

  // TODO: rename e3, e4 => missing1, missing2
  private final E e0;
  private final E e1;
  private final E e2;
  private final E e3;
  private final E e4;

  public SampleElements(E e0, E e1, E e2, E e3, E e4) {
    this.e0 = e0;
    this.e1 = e1;
    this.e2 = e2;
    this.e3 = e3;
    this.e4 = e4;
  }

  @Override
  public Iterator<E> iterator() {
    return asList().iterator();
  }

  @SuppressWarnings("unchecked")
  public static <E> ImmutableSet<E> of(E e1, E e2) {
    return create(e1, e2);
  }

  @SuppressWarnings("unchecked")
  public static <E> ImmutableSet<E> of(E e1, E e2, E e3) {
    return create(e1, e2, e3);
  }

  @SuppressWarnings("unchecked")
  public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4) {
    return create(e1, e2, e3, e4);
  }

  @SuppressWarnings("unchecked")

    MetadataGraphEdge e1;
    MetadataGraphEdge e2;
    MetadataGraphEdge e3;

    // ------------------------------------------------------------------------------------------
    @BeforeEach
    void setUp() throws Exception {
        policy = new DefaultGraphConflictResolutionPolicy();
        e1 = new MetadataGraphEdge("1.1", true, null, null, 2, 1);
        e2 = new MetadataGraphEdge("1.2", true, null, null, 3, 2);