Add CI tests

[Keanu73]

It's kindof remarkable that testing was quite amok for you (#272) but what's even more restraining is the fact that we don't have CI. It would make life so much easier, especially for you (as you're the only active maintainer of the project) as CI would automatically test commits and find any problems with them. We should feed our test cases into CI and let it do the dirty work for us. (Although we would have to be more rigorous and implement every possible bloody test case in existence)