Revamp test suite #156
Description
Our test suite is currently underpowered, and does not sufficiently test the full matrix of all combinations within all features. Ideally, all features should be tested against all supported kinds of repositories.
Currently, all tests can specify the repositories they need, which means they'll usually only test the features against that specific set of inputs. One approach would be to generalize that across a list, and then cross product that with the actual test logic. Another would be to have the test fixture always provide all repositories, since all tests will then use all of them anyways.
One difficulty is that providing the repositories is not sufficient, additionally hashes for pinned values need to also be generated. Currently this is done with the resolveGitCommit bash function in the prelude. Moving that functionality into Nix would probably require IFD, but that would probably be acceptable.