Create a verified fake resolver

[Richard Wall]

twisted.names.test.test_client includes a FakeResolver class used to test the module level lookup? functions in twisted.names.client.

This fake resolver may can be used in place of:

• source:twisted/internet/test/connectionmixins.py FakeResolver
• source:twisted/names/test/test_srvconnect.py FakeResolver

FakeResolver class should be moved to a new module twisted.names.fakeresolver

It needs testing, to ensure that it matches the real IResolver interface; including methods, method signatures, return types and exceptions raised.

Exarkun recommends using fakepwd.py as the best current example of a verified fake:

• source:trunk/twisted/python/fakepwd.py

...and its tests:

• source:trunk/twisted/python/test/test_fakepwd.py

This idea was originally proposed in #3908 but wasn't actually needed for the resolution of that ticket.

[Richard Wall]

(In [39320]) prototype FakeResolver for testing root.Resolver(resolver) and other dns client code. refs #6095, #6379