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Block PRs on Coverage Regression

This guide walks through the complete setup to block pull requests that regress coverage. By the end, the nolapse check will be required to pass before any PR can merge into your default branch.

Prerequisites

Section titled “Prerequisites”
  • nolapse initialised in your repo (nolapse init has been run and baseline.md is committed)
  • A GitHub repository with branch protection available (any plan)

Step 1 — Add the GitHub Actions workflow

Section titled “Step 1 — Add the GitHub Actions workflow”

Create .github/workflows/coverage.yml:

name: Coverage check


on:
  pull_request:


jobs:
  coverage:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0


      - name: Run nolapse
        uses: nolapse/nolapse-action@v1
        with:
          repo-token: ${{ secrets.GITHUB_TOKEN }}
          warn-threshold: "0.5"
          fail-threshold: "1.0"

Key points:

  • fetch-depth: 0 is required so nolapse can read the full git history and the committed baseline.
  • repo-token allows the action to post a coverage summary as a PR comment and set the commit status.
  • warn-threshold and fail-threshold are in percentage points. 1.0 means a 1 percentage-point drop triggers a failure.

For a Python project, add lang: python to the with block:

      - name: Run nolapse
        uses: nolapse/nolapse-action@v1
        with:
          repo-token: ${{ secrets.GITHUB_TOKEN }}
          lang: python
          warn-threshold: "0.5"
          fail-threshold: "1.0"

Step 2 — Commit and push

Section titled “Step 2 — Commit and push”
Terminal window
git add .github/workflows/coverage.yml
git commit -m "ci: add nolapse coverage gate"
git push

Open a pull request. GitHub will pick up the new workflow and run it. The check appears as Coverage check / coverage in the PR checks list.

Step 3 — Enable branch protection

Section titled “Step 3 — Enable branch protection”

Go to your repository on GitHub: Settings → Branches → Add rule (or edit the existing rule for your default branch).

  1. Set Branch name pattern to main (or your default branch name).
  2. Enable Require status checks to pass before merging.
  3. In the search box, type coverage and select Coverage check / coverage.
  4. Enable Require branches to be up to date before merging (recommended — prevents stale-branch bypasses).
  5. Save the rule.

From this point on, any PR that fails the nolapse check cannot be merged until either the coverage regression is fixed or the threshold is adjusted.

How the Check Appears on a PR

Section titled “How the Check Appears on a PR”

When nolapse runs, it posts a comment to the PR and sets a GitHub commit status. An example comment:

## nolapse coverage report


| File | Baseline | PR coverage | Delta | Outcome |
| --- | --- | --- | --- | --- |
| .   | 82.50%   | 81.20%      | -1.30% | fail   |


outcome: fail  delta: -1.30%  fail_threshold: 1.0%

The commit status shows as a red X with the label “Coverage check / coverage” when the outcome is fail, blocking the merge button.

Adjusting Thresholds

Section titled “Adjusting Thresholds”

To change the thresholds, edit the warn-threshold and fail-threshold values in coverage.yml, or set them permanently in nolapse.yaml and remove the flags from the workflow:

nolapse.yaml
lang: go
warn_threshold: 0.5
fail_threshold: 1.0

See Raise Your Coverage Threshold for a guide on incrementally tightening enforcement.

See Also

Section titled “See Also”