Add coverage to CI

Author: tomkins

.github/workflows/ci.yml

@@ -16,9 +16,9 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v5
         with:
-          python-version: '3.13'
-          cache: 'pip'
-          cache-dependency-path: 'requirements/*.txt'
+          python-version: "3.13"
+          cache: "pip"
+          cache-dependency-path: "requirements/*.txt"
       - name: Run tox
         id: matrix
         run: |
@@ -45,8 +45,8 @@ jobs:
         uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python }}
-          cache: 'pip'
-          cache-dependency-path: 'requirements/*.txt'
+          cache: "pip"
+          cache-dependency-path: "requirements/*.txt"
       - name: Run tests
         env:
           PGHOST: localhost
@@ -57,6 +57,13 @@ jobs:
         run: |
           pip install $(grep -E "^(tox|tox-uv)==" requirements/local.txt)
           tox -e ${{ matrix.tox_env }}
+      - name: Upload coverage data
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-data-${{ matrix.tox_env }}
+          include-hidden-files: true
+          path: .coverage.*
+          if-no-files-found: ignore
     services:
       postgres:
         image: postgres:17-alpine
@@ -65,3 +72,30 @@ jobs:
         ports:
           - 5432:5432
         options: --health-cmd pg_isready --health-interval 10s --health-timeout 5s --health-retries 5
+
+  coverage:
+    name: Coverage
+    runs-on: ubuntu-24.04
+    needs: test
+    if: always()
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+          cache: "pip"
+          cache-dependency-path: "requirements/*.txt"
+      - uses: actions/download-artifact@v4
+        with:
+          pattern: coverage-data-*
+          merge-multiple: true
+      - name: Run coverage
+        run: |
+          pip install $(grep -E "^(tox|tox-uv)==" requirements/local.txt)
+          tox -e coverage
+          tox -qq exec -e coverage -- coverage report --format=markdown >> $GITHUB_STEP_SUMMARY