public final void containsKey(@Nullable Object key) {
    check("keySet()").that(checkNotNull(actual).keySet()).contains(key);
  }
@Test
  public void containsKey_failsWithSameToString() {
    expectFailureWhenTestingThat(ImmutableMap.of(1L, "value1", 2L, "value2", "1", "value3"))
        .containsKey(1);
    assertFailureKeys(
        "value of",
        "expected to contain",
        "an instance of",
        "but did not",
        "though it did contain",
        "full contents",
        "map was");
    assertFailureValue("value of", "map.keySet()");
    assertFailureValue("expected to contain", "1");
  }