[mgkimsal]

> Adding tests for an app with no documentation requires a lot of effort.

code tests yes. Assuming it's a web app, probably not too hard. Get something that records the browser interactions, and do the common tasks people do (log in, click links, make a report, etc). Having general things like that automated to ensure you can run them repeatedly to make sure basic stuff didn't break unexpectedly will help provide some confidence when making changes.