@SuppressWarnings("nullness") // test of a bogus call
  public void testSplitNullString() {
    assertThrows(NullPointerException.class, () -> COMMA_SPLITTER.split(null));
  }

  public void testCharacterSimpleSplit() {
    String simple = "a,b,c";
    Iterable<String> letters = COMMA_SPLITTER.split(simple);
    assertThat(letters).containsExactly("a", "b", "c").inOrder();
  }

  /**