ADR 032 — Patch coverage measurement over modified lines

Status

Accepted

Context

Previously, CI enforced --cov-fail-under=63, a global percentage over the entire repository. Global coverage measures the artifact as a whole, so a new module landing at 0% test coverage moves the global percentage by only a fraction of a point, passing the gate undetected.

Decision

1. Patch / Diff Coverage Measurement:
2. Test coverage is measured over the lines touched by the change (git diff against base ref origin/main), rather than solely over the repository as a whole.
3. On a branch with several commits, the diff compares <base_ref>..HEAD, measuring line coverage across all commits on the branch.

4. On a change that only deletes code or contains no added executable Python lines, patch coverage is 100% (exempt / N/A).

5. Global Threshold vs Patch Threshold:

6. We KEEP both thresholds (supplementing global coverage with patch coverage):
   • Global --cov-fail-under=63 acts as a repository-wide safety floor against baseline regression.
   • Patch coverage (target: >=80.0%) guarantees that new and modified executable Python code arrives covered by tests.