public StringSubject factValue(String key) {
    return doFactValue(key, null);
  }
@Test
  public void factValueFailNoSuchKey() {
    Object unused = expectFailureWhenTestingThat(fact("foo", "the foo")).factValue("bar");
    assertFailureKeys("expected to contain fact", "but contained only");
    assertFailureValue("expected to contain fact", "bar");
    assertFailureValue("but contained only", "[foo]");
  }