Proposal: Revive Pytest Jupyter

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I would like to propose bringing the pytest-jupyter project out of archive. We had earlier decided to archive it because the package's use of pytest entry points was causing subtle errors with other pytest plugins (such as pytest-tornasync).

We have had great success in using the fixtures from jupyter_server, but it makes more sense for some of those to be more widely available. We could add them to an existing package like jupyter_core or jupyter_client, but then our tests would depend on a newer version of those libraries.

I think we should bring back pytest-jupyter and remove the pytest entrypoint, and instead make the fixtures usable with pytest_plugins = ["pytest-jupyter"].

We could add the following things to what is already in the repo (which include environment setup and other core fixtures):

• A fork of tornasync with our overrides from jupyter_server
• An echo kernel class and helper fixtures that can be used in testing, which we're already doing in JupyterLab for most tests, which would drastically improve test speed for jupyter_client and jupyter_server, among others.

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We decided in the meeting that we will proceed with this idea, I'm unarchiving the repo now.