assertTrue("An Object should be equal to itself.", collection.equals(collection));
  }

  // Comparisons to null *are* defined.
  @SuppressWarnings("UndefinedEquals")
  public void testEquals_null() {
    // noinspection ObjectEqualsNull
    assertFalse("An object should not be equal to null.", collection.equals(null));
  }

  // A collection should essentially never be equal to a non-collection.
  @SuppressWarnings("UndefinedEquals")

      return unmodifiableNavigableSet((NavigableSet<E>) collection);
    } else {
      return unmodifiableSortedSet((SortedSet<E>) collection);
    }
  }

  @Override
  Collection<V> wrapCollection(@ParametricNullness K key, Collection<V> collection) {
    if (collection instanceof NavigableSet) {
      return new WrappedNavigableSet(key, (NavigableSet<V>) collection, null);
    } else {

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.testing.AbstractCollectionTester;
import org.junit.Ignore;

/**
 * A generic JUnit test which tests {@code size()} operations on a collection. Can't be invoked
 * directly; please see {@link com.google.common.collect.testing.CollectionTestSuiteBuilder}.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible

                  }

                  @Override
                  public SampleElements<Entry<String, Collection<String>>> samples() {
                    return new SampleElements<>(
                        mapEntry("a", (Collection<String>) ImmutableSortedSet.of("alex")),
                        mapEntry("b", (Collection<String>) ImmutableSortedSet.of("bob", "bagel")),

    return emptySet();
  }

  protected Collection<Method> suppressForHashtable() {
    return emptySet();
  }

  protected Collection<Method> suppressForLinkedHashMap() {
    return emptySet();
  }

  protected Collection<Method> suppressForTreeMapNatural() {
    return emptySet();
  }

  protected Collection<Method> suppressForTreeMapWithComparator() {

import com.google.common.collect.testing.features.CollectionSize;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.function.Predicate;
import org.junit.Ignore;

/**
 * A generic JUnit test which tests {@link Collection#removeIf}. Can't be invoked directly; please
 * see {@link com.google.common.collect.testing.CollectionTestSuiteBuilder}.

  protected Collection<Method> suppressForCheckedSet() {
    return emptySet();
  }

  protected Collection<Method> suppressForCheckedSortedSet() {
    return emptySet();
  }

  protected Collection<Method> suppressForAbstractSet() {
    return emptySet();
  }

  protected Collection<Method> suppressForConcurrentSkipListSetNatural() {
    return emptySet();
  }

  protected Collection<Method> suppressForSingletonSet() {
    return emptySet();
  }

  protected Collection<Method> suppressForHashSet() {
    return emptySet();
  }

  protected Collection<Method> suppressForLinkedHashSet() {
    return emptySet();
  }

  protected Collection<Method> suppressForEnumSet() {
    return emptySet();
  }

  protected Collection<Method> suppressForSynchronizedNavigableSet() {

  /*
   * Previously we had a field named list that was initialized to the value of
   * collection in setUp(), but that caused problems when a tester changed the
   * value of list or collection but not both.
   */
  protected final List<E> getList() {
    return (List<E>) collection;
  }

  /**
   * {@inheritDoc}
   *
   * <p>The {@code AbstractListTester} implementation overrides {@link

        UnsupportedOperationException.class,
        () -> collection.removeAll(MinimalCollection.of(e0())));
    expectUnchanged();
    assertTrue(collection.contains(e0()));
  }

  /*
   * AbstractCollection fails the removeAll(null) test when the subject
   * collection is empty, but we'd still like to test removeAll(null) when we
   * can. We split the test into empty and non-empty cases. This allows us to
   * suppress only the former.