Write unit tests

[Ovaday]

I've created a branch for you with 2 tests:

• /tg_bot/tests.py
• /tests/test_helpers.py

They can be launched with python manage.py test and python manage.py test tests/ correspondingly.

What you'll need to do:

• Fix /tg_bot/tests.py to make run with the project. Use https://docs.djangoproject.com/en/4.2/topics/testing/overview/ as a guide.
• Check every .py script in the helpers directory and find scripts that are testable. If there are too little of them, in addition you can test code from the folder open_ai.
• To the defined testable methods write tests inside /tests/test_helpers.py or /tests/test_open_ai.py if applicable.