from twisted.trial.unittest import TestCase
from twisted.internet import defer, reactor
from twisted.internet.defer import DeferredList, Deferred

def deferredException(x):
    d = defer.Deferred()
    reactor.callLater(0.5, d.errback, x * 3)
    return d

class Blah(TestCase):
    def test_blah(self):
        dl = DeferredList([
                deferredException(1),
                deferredException(2),
                deferredException(3),
                ])
        def testGotErrors(result_list):
            for success, result in result_list:
                # These will all succeed.
                self.assertFalse(success)

            # In fact at this point, we have no errors, no reason to suspect anything is wrong.
            # But when the DebugInfo objects are GarbageCollected, they log all three errors
            # and the _LogObserver turns those into unittest ERROR outputs.

            # We can try to clear the logs, but because the errors haven't yet been created
            # clearing the logs results in hair-loss, general screaming, and swearing in comments
            # because the test still errors.
            self.flushLoggedErrors()
        return dl.addCallback(testGotErrors)