@RunWith(JUnit4.class)
public final class InvalidatableSetTest {
  Set<Integer> wrappedSet;
  Set<Integer> copyOfWrappedSet;
  InvalidatableSet<Integer> setToTest;

  @Before
  public void createSets() {
    wrappedSet = new HashSet<>();
    wrappedSet.add(1);
    wrappedSet.add(2);
    wrappedSet.add(3);

    copyOfWrappedSet = ImmutableSet.copyOf(wrappedSet);
    setToTest =

@RunWith(JUnit4.class)
public final class InvalidatableSetTest {
  Set<Integer> wrappedSet;
  Set<Integer> copyOfWrappedSet;
  InvalidatableSet<Integer> setToTest;

  @Before
  public void createSets() {
    wrappedSet = new HashSet<>();
    wrappedSet.add(1);
    wrappedSet.add(2);
    wrappedSet.add(3);

    copyOfWrappedSet = ImmutableSet.copyOf(wrappedSet);
    setToTest =

  @LazyInit @CheckForNull private transient Multiset<K> keys;

  @Override
  public Multiset<K> keys() {
    Multiset<K> result = keys;
    return (result == null) ? keys = createKeys() : result;
  }

  abstract Multiset<K> createKeys();

  @LazyInit @CheckForNull private transient Collection<V> values;

  @Override
  public Collection<V> values() {
    Collection<V> result = values;

  @LazyInit @CheckForNull private transient Multiset<K> keys;

  @Override
  public Multiset<K> keys() {
    Multiset<K> result = keys;
    return (result == null) ? keys = createKeys() : result;
  }

  abstract Multiset<K> createKeys();

  @LazyInit @CheckForNull private transient Collection<V> values;

  @Override
  public Collection<V> values() {
    Collection<V> result = values;

    return new FilteredMultimapValues<>(this);
  }

  @Override
  Map<K, Collection<V>> createAsMap() {
    return Maps.filterKeys(unfiltered.asMap(), keyPredicate);
  }

  @Override
  Multiset<K> createKeys() {
    return Multisets.filter(unfiltered.keys(), keyPredicate);
  }