Add tests to CI pipeline

[krassowski]

Problem

I would like to contribute. I hoped that some tests would run on CI for #210. I see that there is no linting as per:

• Current build doesn't show python code errors in terminal #81 and
• Automate code styling #201

The package appears to have three suites of tests documented in packages/jupyter-ai/README.md:

1. Python tests

(removed note about pip install -e .[tests] not working - it works if run from packages/jupyter-ai)

I see only one commented out test file.

2. Frontend tests

There are only two tests: one skipped and one useless.

3. Integration tests

There is only a smoke test.

Proposed Solution

If tests were written but not commited, commit them. If tests were not written either add a note for the contributors or plan writting them for newly added code? My issue is mostly about managing expectations, I do not think contributors should be expected to debug why tests (which are not there) do not run, and users should now that the package has no tests yet.

Additional context

Jupyter Criteria for official Subprojects include:

• Use solid software engineering with documentation and tests hosted with appropriate technologies (Read The Docs and Travis are examples of technologies that can be used).