'We can chain L{Deferred}s implicitly by adding callbacks that return
L{Deferred}s. When this chaining happens, we record it explicitly as
soon as we can find out about it.'

def test_chainDeferredRecordsImplicitChain(self):

    a = defer.Deferred()
    b = defer.Deferred()
    a.addCallback((lambda ignored: b))
    a.callback(None)
    self.assertIs(a._chainedTo, b)
