The one in https://github.com/solid/test-suite is https://github.com/solid/webid-provider-tests

It's worth noting that it's not perfect, and currently only Nextcloud, NSS and PSS pass this test suite, but this is mainly due to the following:

I think any solid-oidc test suite necessarily needs to use some sort of headless browser to mimic the end-user entering their credentials, clicking on a "Login" button, getting redirected from the app to the IDP to the auth server etc.

We (the test-suite team) have done this for NSS, PSS, and Nextcloud.
For NSS and PSS we used custom node-fetch calls to mimic how the user submits data.
For Nextcloud, we used Puppeteer, which is obviously the more powerful way to do this.
For other implementations, we just haven't gone through the trouble of reverse-engineering their GUI.

Contributions very welcome!

PS: If you're not able to contribute in code, you can also contribute by sponsoring the Independent Solid Test Suite, via Open Collective.

Because Solid-OIDC will likely be just one authentication mechanism for Solid (as opposed to the one-and-only authentication mechanism), I would like to see either a stand-alone suite for Solid-OIDC or else a very modular structure for integration with the existing suites mentioned above.