// Not a valid string
    assertNotWellFormed(-1, 0, -1, 0);
  }

  public void testShardsHaveExpectedRoundTrippables() {
    // A sanity check.
    long actual = 0;
    for (long expected : generateFourByteShardsExpectedRunnables()) {
      actual += expected;
    }
    assertEquals(EXPECTED_FOUR_BYTE_ROUNDTRIPPABLE_COUNT, actual);
  }

  private static String newString(char... chars) {
    return new String(chars);