- make a few trials dirs [TMP]/first [TMP]/second [TMP]/third - fetch trial dirs in order first ['taken'] second third - no more trial dirs left None - test checksum verification - detect wrong checksum ok, got RuntimeError("Checksum mismatch for '[PATH]/trial_test/invalid_checksum/file2' vs. '[PATH]/trial_test/invalid_checksum/checksums.md5' line 2",) - detect missing file ok, got RuntimeError("File listed in checksums file but missing in trials dir: '[PATH]/trial_test/missing_file/file2' vs. '[PATH]/trial_test/missing_file/checksums.md5' line 2",)