tests: Add unit tests for `main.py`

### Why it needs to get done

Adding exit codes resulted in more logic to be moved in `main.py`. Previously, we didn't have unit tests for this file. However, we need to add those now in order to test logic and increase unit test coverage.

### What needs to get done

Add unit tests for `main.py` file.

### When is the task considered done

There are unit tests