Improve reliability of Coverage reporting on CI

[fizyk]

Chore that needs to be done:

• Add newsfragment pipenv run towncrier create [issue_number].[type].rst

Types are defined in the pyproject.toml, issue_number either from issue tracker or the Pull request number

Summary by CodeRabbit

• Chores
  • Enhanced CI coverage reporting with improved multiprocessing support for more reliable test coverage collection.
  • Optimised coverage collection across serial and parallel test execution modes.
  • Updated testing infrastructure dependencies.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR refactors CI coverage reporting by replacing pytest-cov plugin integration with explicit coverage.py invocations. Coverage data is now collected separately for serial and xdist test modes, combined per mode, and exported to distinct XML files for Codecov upload. Local pytest configurations no longer use the --cov flag.

Changes

Coverage reporting refactoring

Layer / File(s)	Summary
Coverage configuration and dependencies .coveragerc, Pipfile	Coverage.py multiprocessing concurrency and parallel execution are enabled; pytest-cov dependency is replaced with coverage package (≥7.0).
Local pytest configuration cleanup pyproject.toml, pyproject.oldest.toml	The --cov flag is removed from pytest addopts in both main and oldest-dependencies configurations.
Docker workflow coverage collection .github/workflows/dockerised-postgres.yml	Docker-based tests now run under explicit coverage run with a dedicated .coverage.docker data file and new combine/export step that generates coverage-docker.xml for Codecov.
PostgreSQL workflow variants with serial and xdist coverage .github/workflows/oldest-postgres.yml, .github/workflows/single-postgres-windows.yml, .github/workflows/single-postgres.yml	Oldest-dependencies, Windows, and main workflows are split into serial and xdist test phases, each using explicit coverage run with distinct data files (.coverage.serial and .coverage.xdist), followed by separate combine/export steps producing coverage-serial.xml and coverage-xdist.xml for Codecov upload.
Release notes newsfragments/+4ed991c2.misc.rst	News fragment documents improved reliability of coverage reporting on CI.

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🎯 2 (Simple) | ⏱️ ~12 minutes

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🐰 A rabbit hops through CI lanes so bright,
Coverage data now splits left and right,
Serial and xdist, each on their own track,
Combined with purpose, no missing the pack!
Reliable reports from parallel test flight. 🚀

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Improve reliability of Coverage reporting on CI' directly reflects the main change: restructuring coverage collection across multiple CI workflows to use explicit coverage data files and combine/export steps instead of relying on pytest's built-in coverage reporting, which improves reliability.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Newsfragment Check	✅ Passed	Newsfragment file +4ed991c2.misc.rst exists with valid 'misc' type, proper format, and content matching PR scope.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch coverage-combine

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[coderabbitai]

🧹 Nitpick comments (1)

newsfragments/+4ed991c2.misc.rst (1)

1-1: 💤 Low value

Consider using the PR number instead of orphan format.

The PR objectives specify using the PR number (1337) for the newsfragment filename. Whilst the orphan format +[hash].[type].rst is acceptable when no dedicated issue exists, the objectives state: "issue_number should be taken from the issue tracker or the pull request number." Consider renaming to 1337.misc.rst to align with the stated convention.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@newsfragments/`+4ed991c2.misc.rst at line 1, The newsfragment filename uses
the orphan/hash format (+4ed991c2.misc.rst); rename this file to use the pull
request number as specified (e.g., 1337.misc.rst) so the issue_number is taken
from the PR instead of the orphan format; update any references to
+4ed991c2.misc.rst in the repo or changelog tooling to the new 1337.misc.rst
name.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@newsfragments/`+4ed991c2.misc.rst:
- Line 1: The newsfragment filename uses the orphan/hash format
(+4ed991c2.misc.rst); rename this file to use the pull request number as
specified (e.g., 1337.misc.rst) so the issue_number is taken from the PR instead
of the orphan format; update any references to +4ed991c2.misc.rst in the repo or
changelog tooling to the new 1337.misc.rst name.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 418b5556-7165-44a5-b2eb-b59139035e60

📥 Commits

Reviewing files that changed from the base of the PR and between d912c6a and 872f852.

📒 Files selected for processing (9)

• .coveragerc
• .github/workflows/dockerised-postgres.yml
• .github/workflows/oldest-postgres.yml
• .github/workflows/single-postgres-windows.yml
• .github/workflows/single-postgres.yml
• Pipfile
• newsfragments/+4ed991c2.misc.rst
• pyproject.oldest.toml
• pyproject.toml