Add unit tests

[justaugustus]

From @lgecse in #157:

Make testing possible with mocking the GH and Jira services. This would make the development faster, and safer.

From: coreos/issue-sync#47

Refactor for improved testability (in preparation for adding unit tests).

From: coreos/issue-sync#41

I'm looking to use this for github -> jira workflow integration. I'd like to add unit tests to ascertain stability and help justify using this open source project at my org. I'll be following up this issue with pull requests as I add unit tests. I'm opening this issue now to start discussion with anyone who's interested in providing feedback/suggestions.

I had a few questions I wanted to ask the maintainers of this project. I figured I would ask here. Could anyone fill me in on the current state of this project? Is it actively being used at CoreOS? How open to external contributions are you?

@\crfeliz this project was started two years ago and at the time we needed to use it because we were migrating our own issues to Jira. Since then, a lot changed for us at CoreOS including our workflows and as a result we are no longer actively using it. I’m maintaining the project but am not actively contributing. However, I would very gladly accept PRs from willing contributors.