Add enforce insert issue number unit tests

[Anarcroth]

Sorry for the delay. Let me know what you think about this :) I'm ready to make any changes.

[CompSciLauren]

Hey! First off, thank you so much for taking the time to write these tests!

So I like what you have here, but I'm having a hard time getting it to work on Travis CI. The build seems to fail because these tests depend on the enforce-insert-issue-number hook being enabled on the repo, and I don't think we can directly rely on that for any tests. Since we need everything to pass on Travis CI, I don't feel comfortable merging this until we figure out how to make Travis CI build successfully.

I spent a lot of time looking into this today but I wasn't able to get it resolved. Unfortunately, I'm about to be really busy for the next couple of weeks and I can't look at this in detail again until roughly Nov 1st - 3rd. Very sorry about that. Please let me know if any of that isn't quite clear or if you have questions. In the meantime, feel free to look into this if you have time, and I'll definitely be looking at this more when I can!

[Anarcroth]

Heyo, no worries, I understand. I was having trouble with passing the build as well. I will try to redo the tests so that the build passes and they don't rely on the repo :)

[zackse]

One approach is something like 68793f5 where we install the hook during @setup and restore the original (if any) during @teardown.

It's not the most elegant, and there is some repetition, but it's a start.

FWIW, the travis build does pass when using this approach. https://travis-ci.org/zackse/awesome-git-hooks/builds/603996943 is a sample build that has the equivalent of PRs #28, #29, #30, and #32 merged.