The test that expects "ya" has "z" too, but "ya" is before and therefore is the right expected answer.
Try using this: std::cout << "* Debug " << "'" << str << "'" << std::endl; when the tests pass, the input will show one after the other, the last one above the error message is the one your code is failing.

You're mixing some tests there, there is no test like that in the Edge Tests.