code: function expectAliSendMessageRequest() {
      return expectSendMessageRequest(aliTestClient.httpBackend).then(function(content) {
          aliMessages.push(content);
          expect(utils.keys(content.ciphertext)).toEqual([bobTestClient.getDeviceKey()]);
          const ciphertext = content.ciphertext[bobTestClient.getDeviceKey()];
          expect(ciphertext).toBeTruthy();
          return ciphertext;
      });
  }
docs: Set an expectation that Ali will send a message, and flush the request
  
  @return {promise} which resolves to the ciphertext for Bob's device.