code: function expectBobSendMessageRequest() {
      return expectSendMessageRequest(bobTestClient.httpBackend).then(function(content) {
          bobMessages.push(content);
          const aliKeyId = "curve25519:" + aliDeviceId;
          const aliDeviceCurve25519Key = aliTestClient.deviceKeys.keys[aliKeyId];
          expect(utils.keys(content.ciphertext)).toEqual([aliDeviceCurve25519Key]);
          const ciphertext = content.ciphertext[aliDeviceCurve25519Key];
          expect(ciphertext).toBeTruthy();
          return ciphertext;
      });
  }
docs: Set an expectation that Bob will send a message, and flush the request
  
  @return {promise} which resolves to the ciphertext for Bob's device.