Run the browser tests in parallel, one job per engine

.github/workflows/checks.yml

@@ -31,9 +31,15 @@ jobs:
       - name: List package contents
         run: npm pack --dry-run
 
-  browser-tests:
+  # One job per engine, in parallel.
+  browser-engines:
+    name: browser-tests (${{ matrix.browser }})
     runs-on: ubuntu-26.04
     timeout-minutes: 10
+    strategy:
+      fail-fast: false # report every engine
+      matrix:
+        browser: [chromium, firefox, webkit]
     steps:
       - uses: actions/checkout@v7.0.1
         with:
@@ -46,7 +52,20 @@ jobs:
       - run: npm ci
 
       # Not cached: Playwright's docs say restoring takes about as long as downloading.
-      - name: Install browsers
-        run: npx playwright install --with-deps --only-shell chromium firefox webkit
+      - name: Install the browser
+        run: npx playwright install --with-deps --only-shell ${{ matrix.browser }}
+
+      - run: npm run test:browsers -- --project="${{ matrix.browser }} *"
 
-      - run: npm run test:browsers
+  # The required check: passes only if every engine passed, so the required
+  # checks stay the same when engines change.
+  browser-tests:
+    needs: browser-engines
+    if: always()
+    runs-on: ubuntu-26.04
+    timeout-minutes: 1
+    steps:
+      - name: Check that every engine passed
+        env:
+          RESULT: ${{ needs.browser-engines.result }}
+        run: test "$RESULT" = success

playwright.config.mjs

@@ -3,20 +3,22 @@ import { defineConfig, devices } from '@playwright/test';
 
 const CI = Boolean(process.env.CI);
 
-// CI runs every engine; locally only Chromium (npx playwright install --only-shell chromium).
+// CI runs every engine (one job each, picked with --project); locally only Chromium
+// (npx playwright install --only-shell chromium).
 const browsers = CI ? ['chromium', 'firefox', 'webkit'] : ['chromium'];
 const devicesByBrowser = { chromium: 'Desktop Chrome', firefox: 'Desktop Firefox', webkit: 'Desktop Safari' };
 
-// Every test runs against both the source and the minified build.
-const files = ['pace.js', 'pace.min.js'];
+// The minified build, which sites load, runs in every engine; the source, which differs only
+// by minification, in Chromium.
+const filesByBrowser = { chromium: ['pace.js', 'pace.min.js'], firefox: ['pace.min.js'], webkit: ['pace.min.js'] };
 
 export default defineConfig({
   testDir: 'tests',
   forbidOnly: CI,
   workers: CI ? 1 : undefined,
   reporter: CI ? [['github'], ['list']] : 'list',
   projects: browsers.flatMap((browser) =>
-    files.map((paceFile) => ({
+    filesByBrowser[browser].map((paceFile) => ({
       name: `${browser} ${paceFile}`,
       use: { ...devices[devicesByBrowser[browser]], paceFile },
     })),