When nesting git repos, is it possible to have the parent track the child?

I'm aware of submodules, but am not sure that will serve this use case.

I've got a repo for a library that's meant to be a framework. In order to write tests, I need to embed a fake app inside test/ that uses the framework.

One of the framework's features is parsing .git/HEAD in the app root to make it easy to display a link to the app's current SHA on github. So, I need to initialize a git repo under test/ in order to test that feature.

Ideally, I'd like the parent repo (which lives in /.git) to track the contents of the nested repo (including /test/.git) as if they were just ordinary files.