I'm not sure that this has anything to do with modules. To me it looks like a question about deployability and dependencies.

Suppose you add a feature to your project in your own sandbox. All tests pass, so you check it in. Unfortunately, your co-worker checks out the project to his sandbox and several tests fail. On inspection, it turns out that you have a different version of a shared library installed and a certain function's behavior has changed in a way that affects your project.

Is there a good, general solution to this problem? I don't think so. I think the easiest answer is still "Know what your dependencies are and test everything you care about that could possibly break."