Add Tests

[unna97]

Is your feature request related to a problem? Please describe.
The current app doesn't have automated tests. This makes it harder to add new changes without verifying it's breaking the app.

Describe the solution you'd like
The tests I would like:

1. Unit Tests
2. Integration Tests
3. System Tests (Functional Tests)
4. Regression Tests

Resources

1. https://docs.djangoproject.com/en/5.0/topics/testing/overview/
2. https://developer.mozilla.org/en-US/docs/Learn/Server-side/Django/Testing