}
    assertInvariants(map);
  }

  public void testSize() {
    assertInvariants(makeEitherMap());
  }

  public void testKeySetRemove() {
    Map<K, V> map;
    try {
      map = makePopulatedMap();
    } catch (UnsupportedOperationException e) {
      return;
    }

    Set<K> keys = map.keySet();