[WAIT] Issue 14: Add Request to ResponsePredicate

[erewok]

Description

This PR does the following:

• Adds the Request to ResponsePredicate so that PredicateFailure can pretty print the request as well as the failing response.

• Removes the Maybe from PredicateFailure (Maybe Request) now that both RequestFailure and ResponseFailure require the request.

• Adds tests for the following predicates: not500 and unauthorizedContainsWWWAuthenticate

Fixes #14

[coveralls]

Coverage increased (+0.3%) to 43.284% when pulling 064b660 on issue-14/req_in_resp_preds into 54a05a5 on master.

[coveralls]

Coverage decreased (-0.1%) to 43.284% when pulling d4f6aa5 on issue-14/req_in_resp_preds into d65abc8 on master.

[erewok]

@jkarni I think this one's ready, I just need a bit of help thinking through any broader implications (CHANGELOG, etc.).

[jkarni]

Hmm, this isn't quite right, I think. The actual requests that resulted in the responses resps are not necessarily req. Rather, they are the requests generated by the RequestPredicates based on req.

[jkarni]

I have to think a little more about this. It feels like it's becoming evident that the Request/ResponsePredicate distinction is somewhat artificial or misleading. Really what's at stake is something like the distinction between request generator (or generator modifiers) and (request + response) predicates. But separating those two too much is also wrong, since usually one wants to generate certain requests in order to check the responses.

[erewok]

I am glad to have your perspective on this. I was wondering about the difference between ResponsePredicate and RequestPredicate when I was working on this PR, but I figured the distinction is still valid as a RequestPredicate needs a Manager in order to actually issue requests.

I have to confess I didn't look closely enough at finishPredicates, so it's a relief that you caught my mistake, which I can see clearly now.

I agree with what you're saying that checking a particular response is really often about a (Request, Response) pair. I was kind of errantly thinking about bifunctors or profunctors when looking at this code this weekend, but I didn't follow the thought very far.

[erewok]

I have been thinking about this PR and I think I'd like to withdraw it. I have some thoughts that I'd like to explore a bit before coming up with a suggestion for representing predicates based on Request + Response versus predicates based only on a Response.

I have been thinking about this in light of this comment from the Predicates module:

-- The idea with all this footwork is to not waste any requests. Rather than
-- generating new requests and only applying one predicate to the response, we
-- apply as many predicates as possible.

While I have some ideas on representing these things, this part is kind of stumping me.