Tests: Use shared fixtures, increase test coverage

[BulkBeing]

Moves remaining tests from unittest to pytest. We were already using pytest as the test runner, but some tests were written with unittest module.

• Upgrade pytest minimum version (we already use latest since we just have >=7.x)
• Use newer features in pytest
• Increase test coverage.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.67%. Comparing base (7a908f2) to head (965d955).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #341   +/-   ##
=======================================
  Coverage   92.67%   92.67%           
=======================================
  Files          67       67           
  Lines        3509     3509           
  Branches      229      229           
=======================================
  Hits         3252     3252           
  Misses        193      193           
  Partials       64       64           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.