BitSet tmp = new BitSet();
    for (char c : chars) {
      tmp.set(c);
    }
    return tmp;
  }

  @GwtIncompatible // java.util.Random, java.util.BitSet
  public void testSmallCharMatcher() {
    CharMatcher len1 = SmallCharMatcher.from(bitSet("#"), "#");
    CharMatcher len2 = SmallCharMatcher.from(bitSet("ab"), "ab");
    CharMatcher len3 = SmallCharMatcher.from(bitSet("abc"), "abc");