Sanitizer.jsm is intended to become our internal one-stop-shop for clearing data. Its (unit) test coverage should be rock solid and extra thorough. The existing tests that test the module directly were all touched in this commit and should be easy to find that way: https://hg.mozilla.org/mozilla-central/rev/092f32e30ed9 That list doesn't inspire a lot of confidence to me, but I might be wrong about it. We currently have most tests in browser/base/content/test/sanitize, though they function very much like unit tests. It would be cool to be able to use xpcshell tests for this as well.