I've held off on writing thorough tests, because getting a good mock WebAuthn authenticator working was a bit daunting. However, Chrome's DevTools protocol now supports virtual authenticators: https://chromedevtools.github.io/devtools-protocol/tot/WebAuthn/

This should make it possible to write fairly robust tests.

I haven't set up a GitHub action testing using the DevTools protocol, so we could use some help if anyone is familiar with how to set that up.