fake response(500) with sinon in post request NodeJs

Question

can anyone help me out creating a fake response (500) for testing my API using "sinon" , am new to nodeJs , i have tried to test where the return status is 201 and it worked however am still not able to make the fake 500 response here is my code , thank you in advance

//knex 

app.post("/api/categories", function (req, rep) {
    knex('categories').insert(req.body)
        .then(() => rep.sendStatus(201).json({ message: "Category inserted" }))
        .catch((err) => {
            console.log(err)
            rep.status(500);
        })
});

// in my test js

var request=require('supertest');
var KnexApp=require('../KnexFolder/app');
var sinon = require("sinon");

describe("POST/users", ()=>{

  describe('when everything is fine and no errors', () => {
    it('should respond with status 201',async () => {
        const res = await request(KnexApp)
        .post('/api/categories')
        .send({
          name:"from test",
          img_id: 5
        })
      expect(res.statusCode).toEqual(201)
     
    })
  })

  describe('when There is internal server error', () => {


    it('should respond with status 500',async () => {
        sinon.stub('/api/categories', "post").throws(
            new Error({
              response: { status: 500},
            })
          );

          expect(res.statusCode).toEqual(500)
     
    })
  })
})

Answer 1

There are two testing strategies:

1. Stub knex, query interface, and the resolved/rejected value. This way is easier than the second way, you don't need to set up a real testing database and populate testing data.

2. As mentioned above, you need to set up a real testing database(run your migration script to create database and tables, create the seed testing data, etc...)

I will use the first way to test your code. Since sinon doesn't support stub a function export defaults by a module. We need to use proxyquire package.

app.js:

const express = require('express');

const knex = require('knex')({
  client: 'mysql',
  connection: {
    host: '127.0.0.1',
    port: 3306,
    user: 'your_database_user',
    password: 'your_database_password',
    database: 'myapp_test',
  },
});
const app = express();

app.use(express.json());
app.post('/api/categories', function (req, rep) {
  console.log(req.body);
  knex('categories')
    .insert(req.body)
    .then(() => rep.sendStatus(201).json({ message: 'Category inserted' }))
    .catch((err) => {
      console.log(err);
      rep.sendStatus(500);
    });
});

module.exports = app;

app.test.js:

const request = require('supertest');
const sinon = require('sinon');
const proxyquire = require('proxyquire');

describe('POST/users', () => {
  describe('when everything is fine and no errors', () => {
    it('should respond with status 201', async () => {
      const queryInterfaceStub = {
        insert: sinon.stub().resolves(),
      };
      const knexStub = sinon.stub().returns(queryInterfaceStub);
      const KnexStub = sinon.stub().returns(knexStub);
      const KnexApp = proxyquire('./app', {
        knex: KnexStub,
      });
      const res = await request(KnexApp).post('/api/categories').send({
        name: 'from test',
        img_id: 5,
      });
      sinon.assert.match(res.statusCode, 201);
    });
  });

  describe('when There is internal server error', () => {
    it('should respond with status 500', async () => {
      const queryInterfaceStub = {
        insert: sinon.stub().rejects(new Error('fake error')),
      };
      const knexStub = sinon.stub().returns(queryInterfaceStub);
      const KnexStub = sinon.stub().returns(knexStub);
      const KnexApp = proxyquire('./app', {
        knex: KnexStub,
      });
      const res = await request(KnexApp).post('/api/categories').send({});

      sinon.assert.match(res.statusCode, 500);
    });
  });
});

Test result:

  POST/users
    when everything is fine and no errors
{ name: 'from test', img_id: 5 }
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:558:11)
    at ServerResponse.header (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/express/lib/response.js:771:10)
    at ServerResponse.send (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/express/lib/response.js:170:12)
    at ServerResponse.json (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/express/lib/response.js:267:15)
    at /Users/dulin/workspace/github.com/mrdulin/expressjs-research/src/stackoverflow/71565119/app.js:20:37
    at processTicksAndRejections (internal/process/task_queues.js:93:5) {
  code: 'ERR_HTTP_HEADERS_SENT'
}
      ✓ should respond with status 201 (436ms)
    when There is internal server error
{}
Error: fake error
    at Context.<anonymous> (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/src/stackoverflow/71565119/app.test.js:27:38)
    at callFn (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/mocha/lib/runnable.js:364:21)
    at Test.Runnable.run (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/mocha/lib/runnable.js:352:5)
    at Runner.runTest (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/mocha/lib/runner.js:677:10)
    at /Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/mocha/lib/runner.js:801:12
    at next (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/mocha/lib/runner.js:594:14)
    at /Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/mocha/lib/runner.js:604:7
    at next (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/mocha/lib/runner.js:486:14)
    at Immediate.<anonymous> (/Users/dulin/workspace/github.com/mrdulin/expressjs-research/node_modules/mocha/lib/runner.js:572:5)
    at processImmediate (internal/timers.js:461:21)
      ✓ should respond with status 500


  2 passing (448ms)