Switch from mocking to actual databases/deployments

Now that we have fixtures for actual databases and deployments (in `conftest.py`), switch the `test_*_main` tests using `Mock` across the project to using the fixtures instead. Use `test_query` and `test_email_generated` for reference.

However, exercise caution when using deployment fixture, as those take quite a while to cleanup, and too many tests using that would make the overall run even longer. Alternatively, consider introducing a "half-way cleaned" fixture for tests requiring only a part of the deployment, which would take a shorter cleanup.