How to use sinon for middleware testing in nodejs?

Question

Trying to test failure scenario for the middleware , v1TransformResponse will throw error on some validation now in unit testing i am not able to get expected result , any idea what is implemented wrong in below test ? i have added the error i am getting.

server.js

app.post('/cvs/v1/drugprice/:membershipId', orchestrateDrugPrice, v1TransformResponse);

v1TransformResponse.js

module.exports = async (req, res) => {
  try {
    const validateResponse = responseHandler(req.drugPriceResponse);
    const transformedResponse = transformResponse(validateResponse);
    const filterDrug = filteredResponse(transformedResponse);
    logDrugPriceResponse('TRANSFORMED_RESPONSE V1', filterDrug);

    res.status(200).send({ drugPrice: filterDrug });
  } catch (error) {
    if (error instanceof AppError) {
      res.status(error.response.status).send(error.response.payload);
    } else {
      res.status(500).send(defaultErrorResponse);
    }
  }
};

main.test.js

const { expect } = require('chai');
const sinon = require('sinon');
const { spy, stub } = require('sinon');
const request = require('supertest');
const app = require('./../../../server/server');
const v1TransformResponse = require('./../../../server/middleware/v1TransformResponse');
const orchestrateDrugPrice = require('./../../../server/middleware/orchestrateDrugPrice');

describe('v1Transform()', () => {
  let status,
    send,
    res;
  beforeEach(() => {
    status = stub();
    send = spy();
    res = { send, status };
    status.returns(res);
  });
  describe('if called with a request that doesn\'t have an example query', () => {
    const req = {
      drugPriceResponse: [{
        'brand': false,
        'drugName': 'Acitretin',
        'drugStrength': '10mg',
        'drugForm': 'Capsule',
        'retailPrice': {
          'copayEmployer': '0',
          'costAnnual': '3',
          'costEmployer': '733.84',
          'costToday': 'N/A',
          'daysSupply': '30',
          'deductible': 'n/a',
          'memberCopayAmount': '30',
          'NDC11': '378702093',
          'penalties': 'N/A',
          'totalDrugCost': '763.84'
        }
      }]
    };
    beforeEach(() => (req, res));
    it('should return error if prices are ommitted', async () => {
      try {
        await v1TransformResponse(req, res);
      } catch (error) {
        expect(error.response).to.deep.equal({
          httpStatus: 500,
          payload: {
            status: 500,
            title: 'Internal Server Error',
            detail: 'Drug prices are not valid'
          }
        });
      }
    });
  });
});

ERROR:

  if called with a request that doesn't have an example query
         should return error if prices are ommitted:
     AssertionError: expected undefined to deeply equal { Object (httpStatus, payload) }

Answer 1

The middleware v1TransformResponse doesn't throw errors in failure case. It calls res.status method. You need to check the parameter passed to it.

it('should return error if prices are ommitted', async () => {
  await v1TransformResponse(req, res);
  expect(res.status.getCall[0].args[0]).to.equal(500);
});