You probably meant to raise that exception. But I wonder whether we even need to bother doing the copy -- why can't we just compare with the image in its original folder (and fail on access if the image is not present)?

Force-pushed a fix to raise.

That is an interesting question, the copying goes back to a5729a5 with the comment "testing bugfix: don't save test results to site-packages".

One nice thing about copying the files is that it puts them (along with the results) next to each other with slightly different names which is something that tools/test_triage.py relies on, but it probably would give a nice speed up (and we can fix test_triage with out too much trouble).