• Tim Peters's avatar
    Improve thread-death error reporting in tests. · adb8ff42
    Tim Peters authored
    Reworked the way some of the ZEO tests use threads, so that unittest is
    more likely to notice the real cause of a failure (which usually occurs in
    a thread), and less likely to latch on to spurious problems resulting from
    the real failure.
    
    Detail:  The TestThread class got the (unittest) test case as an argument,
    and remembered it.  If the run() method saw the thread die with an
    exception, it called testcase.fail() with the formatted exception.  But
    this can't work as apparently intended:  unittest's fail() raises an
    AssertionError then, and the piece of unittest running the test expects
    to catch that exception and append the message to the result object's
    list of failures.  But the piece of unittest running the test isn't on
    *this* thread's call stack!  It's on the main thread's call stack.
    So unittest simply raised an exception that wasn't noticed by anything,
    and the thread died then, leaving a traceback somewhere in the middle
    of the output.  unittest didn't know anything about that, and sometimes
    thought the test passed despite the thread failure.
    
    Alas, when a thread dies like this it's also got a decent chance of
    leaving things in a state where the test's final checking code can't
    succeed, but the checking code doesn't know the thread died either,
    and spurious unittest failures and errors could get reported then.
    
    Reworked things so that only the main thread ever tries to tell
    unittest that a test failed.  A TestThread remembers an exception-
    death now, but doesn't report it until the main thread tries to join
    it.  This way unittest knows the test failed; records and reports
    the true cause of failure; and, because tests generally join all their
    threads before doing their final checking, unittest stops the test
    before final checking if a thread death occurred, and so there's
    less chance of seeing reports of spurious errors and failures.
    adb8ff42
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