DeferredPool tests that the result of the Deferred put into the pool is not obscured.  The completion deferred is not the same deferred, so I wanted to test that I do not break the `chainDeferred` call (that callbacks and errbacks the completion Deferred on result/failure of the pooled Deferred) if a pool is provided.  You are right that it might be overkill though, and certainly if I switch the default implementation of the supervisor to a service, this test case is not needed (since there are tests above that test propagating success and failure to the completion deferred in the default case)