for (char c = 'e'; c < 'z'; c++) {
      assertFalse(len4.matches(c));
    }

    Random rand = new Random(1234);
    for (int testCase = 0; testCase < 100; testCase++) {
      char[] chars = randomChars(rand, rand.nextInt(63) + 1);
      CharMatcher m = SmallCharMatcher.from(bitSet(chars), new String(chars));
      checkExactMatches(m, chars);
    }
  }