}

  private static <T extends @Nullable Object> Entry<T, T> entry(T key, T value) {
    return new AbstractMap.SimpleImmutableEntry<>(key, value);
  }

  public void testCopyOfEmptyMap() {
    ImmutableBiMap<String, Integer> copy =
        ImmutableBiMap.copyOf(Collections.<String, Integer>emptyMap());
    assertEquals(Collections.<String, Integer>emptyMap(), copy);

  }

  public void testOfWithDuplicateKey() {
    assertThrows(IllegalArgumentException.class, () -> ImmutableMap.of("one", 1, "one", 1));
  }

  public void testCopyOfEmptyMap() {
    ImmutableMap<String, Integer> copy =
        ImmutableMap.copyOf(Collections.<String, Integer>emptyMap());
    assertEquals(Collections.<String, Integer>emptyMap(), copy);

  }

  public void testOfWithDuplicateKey() {
    assertThrows(IllegalArgumentException.class, () -> ImmutableMap.of("one", 1, "one", 1));
  }

  public void testCopyOfEmptyMap() {
    ImmutableMap<String, Integer> copy =
        ImmutableMap.copyOf(Collections.<String, Integer>emptyMap());
    assertEquals(Collections.<String, Integer>emptyMap(), copy);