assertThrows(
        IllegalArgumentException.class, () -> base64().withPadChar('#').withSeparator("!#!", 3));
  }

  public void testAtMostOneSeparator() {
    BaseEncoding separated = base64().withSeparator("\n", 3);
    assertThrows(UnsupportedOperationException.class, () -> separated.withSeparator("$", 4));
  }

  public void testBase64() {