test: fix flakiness of certain extension tests (puppeteer#3011)

test/headful.spec.js

@@ -19,6 +19,20 @@ const os = require('os');
 
 const TMP_FOLDER = path.join(os.tmpdir(), 'pptr_tmp_folder-');
 
+function waitForBackgroundPageTarget(browser) {
+  const target = browser.targets().find(target => target.type() === 'background_page');
+  if (target)
+    return Promise.resolve(target);
+  return new Promise(resolve => {
+    browser.on('targetcreated', function listener(target) {
+      if (target.type() !== 'background_page')
+        return;
+      browser.removeListener(listener);
+      resolve(target);
+    });
+  });
+}
+
 module.exports.addTests = function({testRunner, expect, PROJECT_ROOT, defaultBrowserOptions}) {
   const {describe, xdescribe, fdescribe} = testRunner;
   const {it, fit, xit} = testRunner;
@@ -42,19 +56,17 @@ module.exports.addTests = function({testRunner, expect, PROJECT_ROOT, defaultBro
   });
 
   describe('HEADFUL', function() {
-    it('background_page target type should be available', async({browser}) => {
+    it('background_page target type should be available', async() => {
       const browserWithExtension = await puppeteer.launch(extensionOptions);
       const page = await browserWithExtension.newPage();
-      const targets = await browserWithExtension.targets();
-      const backgroundPageTarget = targets.find(target => target.type() === 'background_page');
+      const backgroundPageTarget = await waitForBackgroundPageTarget(browserWithExtension);
       await page.close();
       await browserWithExtension.close();
       expect(backgroundPageTarget).toBeTruthy();
     });
-    it('target.page() should return a background_page', async({browser}) => {
+    it('target.page() should return a background_page', async({}) => {
       const browserWithExtension = await puppeteer.launch(extensionOptions);
-      const targets = await browserWithExtension.targets();
-      const backgroundPageTarget = targets.find(target => target.type() === 'background_page');
+      const backgroundPageTarget = await waitForBackgroundPageTarget(browserWithExtension);
       const page = await backgroundPageTarget.page();
       expect(await page.evaluate(() => 2 * 3)).toBe(6);
       await browserWithExtension.close();