Fix request_version test is not async

Test actually didn't work properly before this fix.
Helper.testOnJsonMsgpack expects an async function test, but the test
was callback based on tried to use done() callback - which wasn't even
provided.

Author: VeskeR

test/rest/request.test.js

@@ -28,17 +28,24 @@ define(['ably', 'shared_helper', 'async', 'chai'], function (Ably, Helper, async
      * @specpartial RSC7e - tests providing a version value in .request parameters
      * @specpartial CSV2c - tests version is provided in http requests
      */
-    Helper.testOnJsonMsgpack('request_version', function (options, _, helper) {
+    Helper.testOnJsonMsgpack('request_version', async function (options, _, helper) {
       const rest = helper.AblyRest(options);
       const version = 150; // arbitrarily chosen
 
+      let savedResolve;
+      let savedReject;
+      let promise = new Promise((res, rej) => {
+        savedResolve = res;
+        savedReject = rej;
+      });
+
       async function testRequestHandler(_, __, headers) {
         try {
           expect('X-Ably-Version' in headers, 'Verify version header exists').to.be.ok;
           expect(headers['X-Ably-Version']).to.equal(version.toString(), 'Verify version number sent in request');
-          done();
-        } catch (err) {
-          done(err);
+          savedResolve();
+        } catch (error) {
+          savedReject(error);
         }
         return new Promise(() => {});
       }
@@ -47,6 +54,7 @@ define(['ably', 'shared_helper', 'async', 'chai'], function (Ably, Helper, async
       rest.http.do = testRequestHandler;
 
       rest.request('get', '/time' /* arbitrarily chosen */, version, null, null, null);
+      await promise;
     });
 
     /**