Bug 1609162 - [remote] Start remote agent only once in remote mochitests r=remote-protocol-reviewers,whimboo

Differential Revision: https://phabricator.services.mozilla.com/D110214

remote/cdp/moz.build

@@ -29,6 +29,7 @@ with Files("domains/**/Target.jsm"):
 
 BROWSER_CHROME_MANIFESTS += [
     "test/browser/browser.ini",
+    "test/browser/component/browser.ini",
     "test/browser/dom/browser.ini",
     "test/browser/emulation/browser.ini",
     "test/browser/input/browser.ini",

remote/cdp/test/browser/browser.ini

@@ -7,7 +7,6 @@ support-files =
   chrome-remote-interface.js
   head.js
 
-[browser_agent.js]
 [browser_cdp.js]
 skip-if = socketprocess_networking
 [browser_httpd.js]

remote/cdp/test/browser/component/browser.ini

@@ -0,0 +1,14 @@
+[DEFAULT]
+tags = remote
+subsuite = remote
+prefs =
+  remote.enabled=true
+support-files =
+  !/remote/cdp/test/browser/chrome-remote-interface.js
+  !/remote/cdp/test/browser/head.js
+  head.js
+
+# This test needs to start and close RemoteAgent several times.
+# It should be the only test in this suite to avoid side-effects with
+# regular tests which reuse a shared RemoteAgent instance.
+[browser_agent.js]

remote/cdp/test/browser/component/head.js

@@ -0,0 +1,11 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/* import-globals-from ../head.js */
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/remote/cdp/test/browser/head.js",
+  this
+);

remote/cdp/test/browser/head.js

@@ -39,6 +39,18 @@ setup and teardown described above.
 
 const add_plain_task = add_task.bind(this);
 
+// Start RemoteAgent lazily and reuse it for all the tests in the suite.
+// Starting and stopping RemoteAgent for every test would trigger race conditions
+// in httpd.js. See Bug 1609162.
+let remoteAgentStarted = false;
+async function startRemoteAgent() {
+  if (!remoteAgentStarted) {
+    await RemoteAgent.listen(Services.io.newURI("http://localhost:9222"));
+    remoteAgentStarted = true;
+    info("Remote agent started");
+  }
+}
+
 this.add_task = function(taskFn, opts = {}) {
   const {
     createTab = true, // By default run each test in its own tab
@@ -47,8 +59,7 @@ this.add_task = function(taskFn, opts = {}) {
   const fn = async function() {
     let client, tab, target;
 
-    await RemoteAgent.listen(Services.io.newURI("http://localhost:9222"));
-    info("CDP server started");
+    await startRemoteAgent();
 
     try {
       const CDP = await getCDP();
@@ -92,9 +103,6 @@ this.add_task = function(taskFn, opts = {}) {
         info("CDP client closed");
       }
 
-      await RemoteAgent.close();
-      info("CDP server stopped");
-
       // Close any additional tabs, so that only a single tab remains open
       while (gBrowser.tabs.length > 1) {
         gBrowser.removeCurrentTab();