Bug 1553784 - Add mochitest for empty list of service workers r=Ola

Differential Revision: https://phabricator.services.mozilla.com/D34154

--HG--
extra : moz-landing-system : lando

devtools/client/application/src/components/WorkerListEmpty.js

@@ -44,7 +44,7 @@ class WorkerListEmpty extends Component {
 
   render() {
     return article(
-      { className: "worker-list-empty" },
+      { className: "worker-list-empty js-worker-list-empty" },
       Localized({
         id: "serviceworker-empty-intro",
         a: a({ className: "external-link", onClick: () => this.openDocumentation() }),

devtools/client/application/test/browser.ini

@@ -22,6 +22,7 @@ support-files =
 [browser_application_panel_list-domain-workers.js]
 [browser_application_panel_list-several-workers.js]
 [browser_application_panel_list-single-worker.js]
+[browser_application_panel_list-workers-empty.js]
 [browser_application_panel_list-unicode.js]
 [browser_application_panel_open-links.js]
 skip-if = true # Bug 1467256

devtools/client/application/test/browser_application_panel_list-workers-empty.js

@@ -0,0 +1,25 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Check that the application panel only displays service workers from the
+ * current domain.
+ */
+
+const EMPTY_URL = (URL_ROOT + "service-workers/empty.html");
+
+add_task(async function() {
+  await enableApplicationPanel();
+
+  const { panel, tab } = await openNewTabAndApplicationPanel(EMPTY_URL);
+  const doc = panel.panelWin.document;
+
+  await waitUntil(() => doc.querySelector(".js-worker-list-empty") !== null);
+  ok(true, "No service workers are shown for an empty page");
+
+  // close the tab
+  info("Closing the tab.");
+  await BrowserTestUtils.removeTab(tab);
+});