Background: I have two test cases: scale > 1 and scale < 1. Files generated for both test cases have the same file name: "scale___1.received.png" (both < and > are replaced with underscore).

This could be improved. For example, instead of replacing each forbidden character with underscore, ApprovalTestNamer could use XML/HTML character references, so that files in the above example would be named scale_>_1.received.png and scale_<_1.received.png.