add integration tests for dummy repo and dummy package

[AndyOGo]

We should be able to test each aspect of the release automatically to make sure that we don't release regressions.

So we should have full featured integration test, including:

• a dummy git repo
• a dummy npm package
• a way of interacting with the CLI script - may be easier to abstract it into an API and script the API instead
• after all tests we should clean up - remove released npm package, git tags, git commits, etc.

If you think this is overkill, we could resort to mock as much as possible, but still we need to verify these functionalities somehow.