Wolfram Workbench includes a nice feature for linking to notebooks:

I have noticed that Mathematica's built-in package editor has been getting better and was wondering if these hyperlink are supported. If not I, think it would be great to have this feature for a future release of Mathematica. Just to be clear, I am talking here about hyperlinks from .m or .wl files to notebooks. Not the other way around which is easy.

Why do I think this is useful? Well, I have a large notebook which autogenerates a package file on every save. This notebook includes tests and I am in the process of switching to editing the package file directly with is better for version control specially with multiple developers. I want to be able to link each function in the package file to a separate notebook with the corresponding tests.