Thank you very much for this valuable tool.

I'd like to propose to add new functionality to compare a file against a stored, known-to-be-correct file. The assertion could be named something like must_match_file. In many cases it's enough for me to use md5sum to verify whether or not a result file has changed at all. However, when I do see that something has changed it would be helpful to see what exactly changed in the output of the test failure. If an assertion like must_match_file existed, then I could be shown how the new result differs from the stored result. Kind of similar to "golden testing", ref https://ro-che.info/articles/2017-12-04-golden-tests.