@Override
  public Collection<V> values() {
    return mInternalMap.values();
  }
@Test
  public void values() {
    String x1 = new String("x");
    String x2 = new String("x");
    assertNull(mMap.put(x1, "z"));
    assertNull(mMap.put(x2, "z"));
    Collection<String> v = mMap.values();
    assertEquals(2, v.size());
    v.forEach(val -> assertEquals("z", val));
    assertEquals("z", mMap.remove(x1));
    assertEquals(1, v.size());
  }