'Assert that C{deferred} does not have a result at this point.
If the assertion succeeds, then the result of C{deferred} is left
unchanged. Otherwise, any L{failure.Failure} result is swallowed.
@param deferred: A L{Deferred<twisted.internet.defer.Deferred>} without
a result.  This means that neither
L{Deferred.callback<twisted.internet.defer.Deferred.callback>} nor
L{Deferred.errback<twisted.internet.defer.Deferred.errback>} has
been called, or that the
L{Deferred<twisted.internet.defer.Deferred>} is waiting on another
L{Deferred<twisted.internet.defer.Deferred>} for a result.
@type deferred: L{Deferred<twisted.internet.defer.Deferred>}
@raise SynchronousTestCase.failureException: If the
L{Deferred<twisted.internet.defer.Deferred>} has a result.'

def assertNoResult(self, deferred):

    result = []
    def cb(res):
        result.append(res)
        return res
    deferred.addBoth(cb)
    if result:
        deferred.addErrback((lambda _: None))
        self.fail(('No    result    expected    on    %r,    found    %r    instead' % (deferred, result[0])))
