Tracking state in the dummyserver

[kevinburke]

I'm trying to work on the retry branch again. To test things I'd like to make a request that fails once or twice and then finally succeeds. However, each of the methods in dummyserver/handlers.py is idempotent, which makes this a little bit tricky.

I'm considering the following:

• Adding a method to handlers.py that tracks state on the class, or resets a class property ("attempts") every test. Then add a method that checks the attempts property and returns a response based on its value.
• Setting a "attempts" cookie on the response and adding cookie parsing to urllib3. Are we even supposed to do this, for example if someone sets a cookie on a 3xx response? However I am not looking forward to adding cookies.
• Mocking _make_request to side effect different things - I know it's not great to use mocks but the mock library does have support for this.
• Using the same approach as the retries test in test_socketlevel.py, which is a bit lower level than I'd like but will do just fine.

[kevinburke]

Actually I have another idea which I will share shortly :)

[shazow]

Why not use socket-level tests?