Report test results & coverage in the CI run summary

.github/workflows/ci.yml

@@ -37,3 +37,40 @@ jobs:
         with:
           name: test-coverage-${{ matrix.node-version }}
           path: test/coverage
+
+  test-coverage:
+    name: Test coverage
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+      - name: Set up Node.js
+        uses: actions/setup-node@395ad3262231945c25e8478fd5baf05154b1d79f # v6.1.0
+        with:
+          node-version: '26.x'
+          cache: 'npm'
+      - name: Install npm dependencies
+        run: npm install
+      - name: Run tests
+        run: |
+          set -o pipefail
+          npm test -- --ci --coverage --runInBand 2>&1 |
+            tee "$RUNNER_TEMP/tests.txt"
+      # Reported in its own step so the summary is still written when the suite
+      # fails, which is when the test results are most worth reading.
+      - name: Report test results & coverage
+        if: ${{ !cancelled() }}
+        run: |
+          {
+            echo '## Tests'
+            echo
+            echo '```'
+            grep -E '^(Test Suites|Tests|Snapshots|Time):' "$RUNNER_TEMP/tests.txt"
+            echo '```'
+            echo
+            echo '## Test coverage'
+            echo
+            echo '```'
+            awk '/^-+\|/ { f = 1 } /^Test Suites:/ { f = 0 } f' "$RUNNER_TEMP/tests.txt"
+            echo '```'
+          } >> "$GITHUB_STEP_SUMMARY"