Throw err when beforeEach.withApp is not called

Author: faridnsh

Diff for: lib/helpers.js

@@ -236,6 +236,10 @@ _describe.whenCalledRemotely = function(verb, url, data, cb) {
       var methodForVerb = verb.toLowerCase();
       if(methodForVerb === 'delete') methodForVerb = 'del';
 
+      if (this.request === undefined) {
+          throw new Error('App is not specified. Please use lt.beforeEach.withApp to specify the app.');
+      }
+
       this.http = this.request[methodForVerb](this.url);
       delete this.url;
       this.http.set('Accept', 'application/json');