Unit Test expecting 57, 123; code review

[gaulouis]

Hello,

Inspiring on C ++ test for my unit tests in C, I noticed an error in the expecting result. Maybe the +1 has no effect?

In https://github.com/antlr/antlr4-cpp/blob/master/antlr4cpp/antlr/test/test_interval_set.cpp

        void test_mixed_ranges_and_elements()
        {
            interval_set s;
            s.insert(1);
            s.insert(std::make_pair(L'a',L'z'+1));
            s.insert(std::make_pair(L'0',L'9'+1));
            std::wstring expecting = L"{1, 48..57, 97..122}";
        }

by comparison with Java implementation

        IntervalSet interval_set = new IntervalSet();
        interval_set.add(1);
        interval_set.add('a', 'z'+1);
        interval_set.add('0', '9'+1);
        String str = interval_set.toString();
        String expecting = "{1, 48..58, 97..123}";

PS:
C ++ operator overloading is friendly

    interval_set s;
    s << 1;// s+1 is ambigus
    s << interval('a', 'z'+1);
    s &= interval('0', '9'+1);
    s |= interval('0', '9'+1);

    std::cout << s << std::endl;