How to properly test Custom Plugins

[Erik-Outreach]

I'm trying to write automated tests around my custom plugin, but couldn't find much documentation on how to do it, so I'm bringing my ideas and proposing a discussion topic, so we can find together what's the best approach to testing custom plugins.

The plugin I have in mind doesn't affect the cypress-driver but just the cypress-server package. So in this case, I don't need to worry about testing browser related stuff, and I see a few approaches I could use to test it:

1. Setup a cypress folder with that custom plugin available, start cypress from mocha test (via moduleApi) and assert it externally.

This is the main approach I've been using but it's a bit cumbersome. For each new plugin I want to write, I need to create a folder (or reuse a single-folder approach with env variable turning plugins on and off). It also requires to expose whatever I need to assert externally, and sometimes mocha results files are suitable, but sometimes not and requires a bit of hacking (output files or something).

2. Mock cypress-server.

When a plugin that doesn't require much of cypress itself to test (node only), then you could mock some part of it. For instance for plugin I need to assert behaviour plugged to 'before:spec', so a bit of decomposition and simulating the invocation of 'before:spec' could get me there. This doesn't require the file setup and is self-contained but doesn't really test it along with cypress.

This possibility takes me to my third alternative which I find more promising.

3. Test along with cypress-server code.

Inspired by event-tests case, I think it could work by installing a plugin on the fly and executing the event from cypress-server package. With this, we'd have a self-contained test which tests the plugin along with cypress without all the setup from step 1.

Unfortunately cypress-server isn't made public so we can't install in node project to consume the methods.

[LR;DR]:

• I could find specific docs about writing tests for plugins.
• Making cypress-server package public could be the way to allow better tests for custom plugins.

Thanks,
Erik Witkowski