Infrastructure for unit tests

[dokterbob]

Is your feature request related to a problem? Please describe. While working on a PR to improve server side rendering (#1091) of the index page, we discovered there's no infrastructure/skaffolding for unit tests.

Describe the solution you'd like Basic infrastructure and CI integration for unittests, something like pytest, so we can rapidly iterate on backend features without breaking compatibility, fostering better collaboration and API stability.

Describe alternatives you've considered Using Cypress E2E testing to test backend features. Integration tests are great but it overcomplicates things when it comes to clear backend features.

Additional context https://circleci.com/blog/unit-testing-vs-integration-testing/