Add unit test

[tmigot]

To make sure everything work when upgrading a release for instance

[dpo]

@MaxenceGollier Can you think of useful unit tests here? Sample benchmarks, I suppose?!

[MaxenceGollier]

@dpo, I think ideally, we should test this on a real GitHub repository.

Perhaps we could build a fake JSO GitHub repo where we can test JSO actions like those ?