public void testGetOnlyElement_noDefault_valid() {
    Iterator<String> iterator = singletonList("foo").iterator();
    assertThat(getOnlyElement(iterator)).isEqualTo("foo");
  }

  public void testGetOnlyElement_noDefault_empty() {
    Iterator<String> iterator = emptyIterator();
    assertThrows(NoSuchElementException.class, () -> getOnlyElement(iterator));
  }

  public void testGetOnlyElement_noDefault_valid() {
    Iterator<String> iterator = singletonList("foo").iterator();
    assertThat(getOnlyElement(iterator)).isEqualTo("foo");
  }

  public void testGetOnlyElement_noDefault_empty() {
    Iterator<String> iterator = emptyIterator();
    assertThrows(NoSuchElementException.class, () -> getOnlyElement(iterator));
  }

  }

  public void testGetOnlyElement_noDefault_valid() {
    Iterable<String> iterable = singletonList("foo");
    assertThat(getOnlyElement(iterable)).isEqualTo("foo");
  }

  public void testGetOnlyElement_noDefault_empty() {
    Iterable<String> iterable = emptyList();
    assertThrows(NoSuchElementException.class, () -> getOnlyElement(iterable));
  }

  public void testGetOnlyElement_noDefault_multiple() {