Make the code testable

[mlazowik]

Most of the existing tests are slow and rely heavily on running shell processes. Source itself also relies on shell, for example for git. This makes testing hard, especially when you'd want to mock something like git push.

In current tests git push always fails and it's ignored. There is no positive test for --post-success. I need to add a regression test for --post-success failing, for now I'll add a --mock-push option, because any other way requires significant changes, like:

• use nodegit
• make it possible to call the whole program from js instead of doing shell.exec (this will make mocking components possible)

[leonardoanalista]

Hi Michal, thanks for your input. You are right. All unit tests are actually integration. They test against a real git repo. It is very hard (impossible) to test and mock post success as it will never succeed. Our friend Brett U added post success flag not too long ago. It was in the latest release.
I had a quick look at nodegit. It looks good. As far as I remember, semantic-release use to use it too.
This is a refactoring for sure. Regarding to the behaviour changes you suggested, we can discuss in the previous issue you created.