tests: Spy on socket.io messages as early as possible

src/static/js/pad.js

@@ -311,14 +311,21 @@ const handshake = async () => {
     }
   });
 
-  await new Promise((resolve) => {
+  await Promise.all([
+    new Promise((resolve) => {
       const h = (obj) => {
         if (obj.accessStatus || obj.type !== 'CLIENT_VARS') return;
         socket.off('message', h);
         resolve();
       };
       socket.on('message', h);
-  });
+    }),
+    // This hook is only intended to be used by test code. If a plugin would like to use this hook,
+    // the hook must first be promoted to officially supported by deleting the leading underscore
+    // from the name, adding documentation to `doc/api/hooks_client-side.md`, and deleting this
+    // comment.
+    hooks.aCallAll('_socketCreated', {socket}),
+  ]);
 };
 
 /** Defers message handling until setCollabClient() is called with a non-null value. */

src/tests/frontend/helper.js

@@ -99,6 +99,16 @@ const helper = {};
       hookFns: {},
     }, opts);
 
+    // Set up socket.io spying as early as possible.
+    /** chat messages received */
+    helper.chatMessages = [];
+    /** changeset commits from the server */
+    helper.commits = [];
+    /** userInfo messages from the server */
+    helper.userInfos = [];
+    if (opts.hookFns._socketCreated == null) opts.hookFns._socketCreated = [];
+    opts.hookFns._socketCreated.unshift(() => helper.spyOnSocketIO());
+
     // if opts.params is set we manipulate the URL to include URL parameters IE ?foo=Bah.
     let encodedParams;
     if (opts.params) {
@@ -171,27 +181,6 @@ const helper = {};
     helper.padOuter$.fx.off = true;
     helper.padInner$.fx.off = true;
 
-    /*
-     * chat messages received
-     * @type {Array}
-     */
-    helper.chatMessages = [];
-
-    /*
-     * changeset commits from the server
-     * @type {Array}
-     */
-    helper.commits = [];
-
-    /*
-     * userInfo messages from the server
-     * @type {Array}
-     */
-    helper.userInfos = [];
-
-    // listen for server messages
-    helper.spyOnSocketIO();
-
     return opts.id;
   };