anchor.diff:  
   main() {
     test.group("arcfour", () {
  -    test.test("operate", () {
  +    test.test("operateA", () {
         List<int> key = Hex.decodeWithNew("0xABCDEF");
         List<int> value = Hex.decodeWithNew("0xA1B2C3D4E5F6A7B8C9");
   //      List<int> result = Hex.decodeWithNew();
  
positive.code:       ARCFOUR.operate(value, 2, value.length - 2, state, 2, stateIJ, 2, output, 2);
        test.expect(Hex.encodeWithNew(output.sublist(2)), "0x91b44728ff906c143d");
      });
    });
  }
  
negative.code:       test.expect(Hex.encodeWithNew(output), "0x91b44728ff906c143d");
      });
  
      test.test("operateB", () {
        List<int> key = [0, 0];
        key.addAll(Hex.decodeWithNew("0xABCDEF"));
        List<int> value = [0, 0];
  