public void testRemoveKeyRemovesFromInverse() {
    getMap().remove(k0());
    expectMissing(e0());
  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testRemoveKeyFromKeySetRemovesFromInverse() {
    getMap().keySet().remove(k0());
    expectMissing(e0());
  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)

  private void assertZeroToZero() {
    assertSetCount(e3(), 0);
  }

  private void assertOneToOne() {
    assertSetCount(e0(), 1);
  }

  private void assertThreeToThree() {
    initThreeCopies();
    assertSetCount(e0(), 3);
  }

  @CollectionFeature.Require(SUPPORTS_ADD)
  public void testSetCount_zeroToZero_addSupported() {
    assertZeroToZero();
  }

  public void testContainsAllMultisetIgnoresFrequency() {
    assertTrue(getMultiset().containsAll(getSubjectGenerator().create(e0(), e0(), e0())));
  }

  @CollectionSize.Require(absent = ZERO)
  public void testContainsAllListIgnoresFrequency() {
    assertTrue(getMultiset().containsAll(asList(e0(), e0(), e0())));
  }

  public void testContainsAllMultisetIgnoresFrequency() {
    assertTrue(getMultiset().containsAll(getSubjectGenerator().create(e0(), e0(), e0())));
  }

  @CollectionSize.Require(absent = ZERO)
  public void testContainsAllListIgnoresFrequency() {
    assertTrue(getMultiset().containsAll(asList(e0(), e0(), e0())));
  }

public class SampleElements<E extends @Nullable Object> implements Iterable<E> {
  // 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

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testElementSetReflectsRemove() {
    Set<E> elementSet = getMultiset().elementSet();
    assertTrue(elementSet.contains(e0()));
    getMultiset().removeAll(singleton(e0()));
    assertFalse(elementSet.contains(e0()));
  }

  @CollectionSize.Require(absent = ZERO)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testElementSetRemovePropagatesToMultiset() {

    int initialSize = collection.size();
    assertTrue("remove(present) should return true", collection.remove(e0()));
    assertEquals(
        "remove(present) should decrease a collection's size by one.",
        initialSize - 1,
        collection.size());
    expectMissing(e0());
  }

  @CollectionFeature.Require({SUPPORTS_REMOVE, FAILS_FAST_ON_CONCURRENT_MODIFICATION})
  @CollectionSize.Require(SEVERAL)

    assertNull(navigableSet.pollFirst());
  }

  @CollectionSize.Require(ZERO)
  public void testEmptySetNearby() {
    assertNull(navigableSet.lower(e0()));
    assertNull(navigableSet.floor(e0()));
    assertNull(navigableSet.ceiling(e0()));
    assertNull(navigableSet.higher(e0()));
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ZERO)
  public void testEmptySetPollLast() {

  private void assertZeroToZero() {
    assertSetCount(e3(), 0);
  }

  private void assertOneToOne() {
    assertSetCount(e0(), 1);
  }

  private void assertThreeToThree() {
    initThreeCopies();
    assertSetCount(e0(), 3);
  }

  @CollectionFeature.Require(SUPPORTS_ADD)
  public void testSetCount_zeroToZero_addSupported() {
    assertZeroToZero();
  }

  public void testAddAll_withDuplicates() {
    MinimalCollection<E> elementsToAdd = MinimalCollection.of(e0(), e1(), e0(), e1());
    assertTrue("addAll(hasDuplicates) should return true", getList().addAll(elementsToAdd));
    expectAdded(e0(), e1(), e0(), e1());
  }