Unit testing your code with this Apps Script Unit test library as you go along will makes it easy to immediately catch errors, and keeping a running test repertoire ensures that you don’t break anything.
When you start developing more complex Google Workspace solutions like add-ons and Chat apps it’s worth considering how you will test, debug and refactor your code. As noted in this post from Bruce Mcpherson the Apps Script community has published a number of different solutions/approaches to unit tests, a number of these appearing in Pulse. This latest post from Bruce looks at the bmUnitTest library he has developed highlighting how it can be set up and used.
Source: Simple but powerful Apps Script Unit Test library – Desktop Liberation
Member of Google Developers Experts Program for Google Workspace (Google Apps Script) and interested in supporting Google Workspace Devs.