Write tests

[yarons]

Due to some recent request we've been looking some popular options to conduct Python tests.

Apparently there are many frameworks but FastAPI suppports Pytest natively:
https://fastapi.tiangolo.com/tutorial/testing/

So we will need to add tests per function and create a test workflow to make sure we're getting the expected results out of the system.

Set of the tests for implementation:

1. Succesful login.
2. Adding a user.
3. Inviting cars at a specific date.
4. Modify the number of invited cars and expected date/time.
5. Removing an invitation.
6. Promoting user to guard.
7. Increasing the number of admitted cars as guard.
8. Download all past events.

This is an async testing example:
https://testdriven.io/blog/fastapi-crud/