Reftests currently do not deal well with a missing file: If the file in a "load" test, or the first file in a "!=" or "==" test, is missing, you get TEST-UNEXPECTED-FAIL || EXCEPTION: ... in the log and the test run is abandoned at that point. It should detect NS_ERROR_FILE_NOT_FOUND and go on to the next test. Worse, if the *second* file (the reference) in a != or == test is missing, the test *hangs* with the reftest window showing the "file not found" screen. I'm not sure why there's a difference there.
It should definitely *always* be a test failure (even if marked "fails"), though.
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