TypeError mocking express response object

Question

I'm currently trying to write a test using sinon and sinon-express-mock to mock an incorrect request and then call a validation function in my application, ensuring that the validation function returns the correct response status (400). However, currently I am getting the error TypeError: Cannot read property 'send' of undefined. I thought send would be mocked along with the rest of the res object, but if not how can I accomplish this? Thanks in advance.

The function I am testing:

export const validateItemRequest = (req, res) => {
    if (!req.query.number) {
        return res.status(400).send('Number not specified');
    } else if ( req.query.number % 1 !== 0) {
        return res.status(400).send('Incorrect number syntax');
    } 
};

The test code:

describe('item', function() {

    it('should only accept valid requests', function() {

        const itemRequest = {
            query: {
                number: 'abcde',
            },
        };

        const req = mockReq(request);
        const res = mockRes();

        itemController.validateItemRequest(req, res);

    });
});

Answer 1

sinon-express-mock currently does not support chaining. There's an open issue to add chaining support, but the methods currently don't return the object making it impossible to chain from res.status to send.

I only needed a few of the response methods for my test, so I made my own response spy like this:

var response = {  
  status: sinon.spy(function() { return response; }),  
  send: sinon.spy(),  
  sendStatus: sinon.spy(),
  reset: function() {
    for (var method in this) {
      if (method !== 'reset') {
        this[method].reset();
      }
    }
  }
};

Notice I only return the response from status since you shouldn't chain off send and sendStatus.

Answer 2

response = { 
   json:(obj) => { response.body = obj },
   status:function(status) {
     response.statusValue = status;
   return this;
 }