Potential Middleware: Test module

[paulbellamy]

It might be nice to have a "Test" middleware, where requests could be injected into the app stack, and the responses given extra information about what got called, etc...

Other Thoughts:

• I'm not 100% sure if this is really needed, since we can do: stack.Compile(handler), and then pass that an Env, or do stack.HandlerFunc(handler), and pass that an http.Request.