test: fix flaky test (#1132)

Author: OrKoN

tests/tools/pages.test.ts

@@ -162,13 +162,18 @@ describe('pages', () => {
 
           assert.ok(extensionId);
 
-          const _sidePanelPage = await context.newPage();
-          await _sidePanelPage.pptrPage.goto(
+          const sidePanelPage = await context.newPage();
+          await sidePanelPage.pptrPage.goto(
             `chrome-extension://${extensionId}/sidepanel.html`,
           );
 
           await context.waitForTextOnPage(['Side Panel']);
 
+          // Wait for service worker used in the snapshot.
+          await context.browser.waitForTarget(
+            target => target.type() === 'service_worker',
+          );
+
           const listPageDef = listPages({
             categoryExtensions: true,
           } as ParsedArguments);