assertThat(expected)
        .hasMessageThat()
        .isEqualTo("expected one element but was: <one, two, three, four, five, ...>");
  }

  public void testGetOnlyElement_withDefault_singleton() {
    Iterator<String> iterator = singletonList("foo").iterator();
    assertEquals("foo", getOnlyElement(iterator, "bar"));
  }

  public void testGetOnlyElement_withDefault_empty() {