Integration tests for adapters

[penx]

It would be good to have a way to run a set of integration tests against each adapter.

While working on the google cloud functions adapter I was able to temporarily switch the fixtures to use my adapter and run the existing integration tests, but this isn't done in a way that could be merged in:

penx@a9d8fa6

I'm happy to work on this but open to suggestions on if it's wanted and how to approach it.

[MichaelDeBoey]

I think it's a great idea to have tests running against all different adapters.

We should make sure to be able to test tiny differences though.