Decide on failMessage

In reply to https://github.com/maxogden/tape-spawn/pull/7#issuecomment-114178145:

yes the failMessage is a little weird... it is currently there to handle the case where the output did not match but you want the failure message to say something specific instead of just did not match.

If it passes it uses message, if it fails it uses failMessage which includes the entire output buffer, mostly because .match succeeds I didn't want it to print out the entire output buffer. I am open to suggestions on making this better. Maybe in the event of a failure it can just append the output buffer to the end of message and then we could get rid of failMessage

Hmm, I’ve never found myself wanting to print another message if a test fails.

If I need to dump some debug info, I just use console.dir or similar stuff. With the beauty of TAP and some reporters like tap-spec v2 this info will be shown alongside the failed test.

Start by reviewing the existing failMessage and message behavior described in the issue and the linked pull request discussion. Decide whether failMessage should remain or whether failures should append the output buffer to message; done requires an agreed behavior and corresponding implementation scope.