'Any recorded chaining is cleared once the chaining is resolved, since
it no longer exists.
In other words, if one L{Deferred} is recorded as depending on the
result of another, and I{that} L{Deferred} has fired, then the
dependency is resolved and we no longer benefit from recording it.'

def test_explicitChainClearedWhenResolved(self):

    a = defer.Deferred()
    b = defer.Deferred()
    b.chainDeferred(a)
    b.callback(None)
    self.assertIsNone(a._chainedTo)
