docs(testing): add regression test tracking policy #176

OSSF Silver Criterion

regression_tests_added50 (MUST) — At least 50% of bug fixes must include a regression test.

Description

Define a regression test tracking policy that ensures at least 50% of bug-fix PRs include a regression test. Issue #146 covers adding a regression test checkbox to the PR template; this issue covers the policy definition, tracking label, and measurement mechanism.

Acceptance Criteria

• regression-test label is created in the repository
• Policy is documented in CONTRIBUTING.md or the test policy document (docs(test-policy): create formal test policy document #145)
• Policy defines: when regression tests are required, how to track compliance, what counts as a regression test
• Bug-fix PRs are expected to check the regression test checkbox and apply the label
• A mechanism exists to measure the 50% target (e.g., label-based query, CI check)

Implementation Guidance

1. Create regression-test label (color suggestion: #B60205, description: "PR includes regression test for a bug fix").

2. Add policy to CONTRIBUTING.md or test policy document:

## Regression Test Policy

Bug-fix pull requests should include a regression test that verifies the fix and
prevents the bug from reoccurring. Our target is for at least 50% of bug-fix PRs
to include regression tests.

When submitting a bug fix:
1. Check the "Regression test included" checkbox in the PR template
2. Apply the `regression-test` label if a test is included
3. If no regression test is feasible, explain why in the PR description

3. Add a periodic query to measure compliance:
   • PRs with label bug AND label regression-test / PRs with label bug >= 50%

References

• Related: docs(pr-template): add regression test requirement for bug fixes #146 (PR template regression checkbox)
• Research: .copilot-tracking/research/2026-02-07-ossf-silver-gaps-detail-research.md — regression_tests_added50

Relationships

• Builds on docs(pr-template): add regression test requirement for bug fixes #146 (PR template)
• Related to docs(test-policy): create formal test policy document #145 (test policy document)
• IS018 tracks this issue