Representing chained methods and members Typescript through Mocha tests

Question

I am testing a node.js controller file using mocha and chai and i'm unable to mock out the response object in my test

TestController.ts

export class TestController {

    static async getTest(req:any, res:any, next:object) {
        console.log("Test");
        //some code here
        res.status(200).json(result.rows);
    }

and this works perfectly fine when I call the API, returns the right response etc. But when I try to test this Controller, here is what I have for my test file

Test.ts

it('Get Test method', async function () {
    let req = {params: {testid: 12345}};
    let res:any = {
      status: function() { }
    };

    res.json = '';
    let result = await TestController.getTest(req, res, Object);
});

I am not sure how to represent the response object here. If I just declare the variable res in the following way

let res:any;

I see the following error in my test

TypeError: Cannot read property 'json' of undefined

I am not sure how my response data structure res should be for making this test work.

Answer 1

You should use sinon.stub().returnsThis() to mock the this context, it allows you to call chain methods.

E.g.

controller.ts:

export class TestController {
  static async getTest(req: any, res: any, next: object) {
    console.log('Test');
    const result = { rows: [] };
    res.status(200).json(result.rows);
  }
}

controller.test.ts:

import { TestController } from './controller';
import sinon from 'sinon';

describe('61645232', () => {
  it('should pass', async () => {
    const req = { params: { testid: 12345 } };
    const res = {
      status: sinon.stub().returnsThis(),
      json: sinon.stub(),
    };
    const next = sinon.stub();
    await TestController.getTest(req, res, next);
    sinon.assert.calledWithExactly(res.status, 200);
    sinon.assert.calledWithExactly(res.json, []);
  });
});

unit test results with 100% coverage:

  61645232
Test
    ✓ should pass


  1 passing (14ms)

---------------|---------|----------|---------|---------|-------------------
File           | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
---------------|---------|----------|---------|---------|-------------------
All files      |     100 |      100 |     100 |     100 |                   
 controller.ts |     100 |      100 |     100 |     100 |                   
---------------|---------|----------|---------|---------|-------------------