public void testNullInput() {
    UnicodeEscaper e = SIMPLE_ESCAPER;
    assertThrows(NullPointerException.class, () -> e.escape((String) null));
  }

  public void testBadStrings() {
    UnicodeEscaper e = SIMPLE_ESCAPER;
    String[] BAD_STRINGS = {
      String.valueOf(Character.MIN_LOW_SURROGATE),
      Character.MIN_LOW_SURROGATE + "xyz",
      "abc" + Character.MIN_LOW_SURROGATE,