Set up testing logic

Closes #5 (closed)

Description

This MR adds the testing logic and currently only holds a dummy test to see if the implementation works.

Inspiration taken from:

https://gitlab.developers.cam.ac.uk/uis/devops/fastapi-boilerplate/-/blob/main/.gitlab-ci.yml?ref_type=heads

But with the adaption to set .python:versions: ["3.11"] instead of setting parallel: null (which did not pass linting).