GitHub Classroom
Just on a minor note. Having taught programming classes in the past, don't use automated testing for grading, or at least not fully.First of, there is a lot more to judge in a program than just the correctness of its output. Is the code readable ? Re-usable ? Did the student understood the core concept of the language and used them correctly ? 
I saw some student fail to produce a correct program but had a well organized code. On the other hand, one of my student once created a program that was just made of switch instruction in switch instruction (up to 5 level of switches) and spread for more than 3000 lines, just because he failed to understand how function where working.You can try to plug a linter in your testing stack, a quality gate, all kind of software to measure the code quality, but it will never be truly fair. It will make your evaluation a game where the student challenge is not understanding the concept of the class, but instead, understanding the rules of the various test you put in place. And those rules tend to be even more arbitrary with than the teacher himself.Trying to automate grading is an engineer trying to apply its vision to education, and it my honest opinion, it is an awful idea. Providing tools to facilitate education is awesome, trying to automate education is a dystopia.