return ('a' <= cp && cp <= 'z') || ('A' <= cp && cp <= 'Z') || ('0' <= cp && cp <= '9')
              ? null
              : ("[" + String.valueOf(cp) + "]").toCharArray();
        }
      };

  public void testNopEscaper() {
    UnicodeEscaper e = NOP_ESCAPER;
    assertThat(escapeAsString(e, TEST_STRING)).isEqualTo(TEST_STRING);
  }

  public void testSimpleEscaper() {
    UnicodeEscaper e = SIMPLE_ESCAPER;
    String expected =