IdentityHashMap<Integer, Integer> map = Maps.newIdentityHashMap();
    assertEquals(emptyMap(), map);
  }

  public void testConcurrentMap() {
    ConcurrentMap<Integer, Integer> map = Maps.newConcurrentMap();
    assertEquals(emptyMap(), map);
  }

  public void testTreeMap() {
    TreeMap<Integer, Integer> map = Maps.newTreeMap();
    assertEquals(emptyMap(), map);
    assertThat(map.comparator()).isNull();

    return new LinkedHashMap<>(capacity(expectedSize));
  }

  /**
   * Creates a new empty {@link ConcurrentHashMap} instance.
   *
   * @since 3.0
   */
  public static <K, V> ConcurrentMap<K, V> newConcurrentMap() {
    return new ConcurrentHashMap<>();
  }

  /**
   * Creates a <i>mutable</i>, empty {@code TreeMap} instance using the natural ordering of its
   * elements.
   *

    return new LinkedHashMap<>(capacity(expectedSize));
  }

  /**
   * Creates a new empty {@link ConcurrentHashMap} instance.
   *
   * @since 3.0
   */
  public static <K, V> ConcurrentMap<K, V> newConcurrentMap() {
    return new ConcurrentHashMap<>();
  }

  /**
   * Creates a <i>mutable</i>, empty {@code TreeMap} instance using the natural ordering of its
   * elements.
   *