Add test for subscribe barrier behavior

static/test.js

@@ -274,6 +274,26 @@ test('getMessages/subscribe', function() {
   cosmo.shutdown();
 });
 
+asyncTest('subscribe barrier', function() {
+  expect(2);
+
+  var subject = randstring();
+  var message = randstring();
+
+  var cosmo = new Cosmopolite({}, null, randstring());
+
+  cosmo.sendMessage(subject, message).then(function() {
+    cosmo.subscribe(subject, -1).then(function() {
+      // We are validating that the message event generated by the subscribe
+      // call has already been processed by the time this promise fires
+      equal(cosmo.getMessages(subject).length, 1, 'one message');
+      equal(cosmo.getMessages(subject)[0]['message'], message, 'message matches');
+      cosmo.shutdown();
+      start();
+    });
+  });
+});
+
 
 module('dev_appserver only');