Jest expect an object with functions inside

Question

I am writing a Jest test in which I call a function and expect an object in return as follows:

const repository = container => {

  const makeBooking = (user, booking) => {
    'make booking function called'
  }

  const generateTicket = (paid, booking) => {
    console.log('generate ticket function called')
  }

  const getOrderById = orderId => {
    console.log('get order by ID called')
  }

  const disconnect = () => {
    console.log('disconnect method called')
  }

  return {
    makeBooking,
    getOrderById,
    generateTicket,
    disconnect
  }
}

All of these functions are now samples for the sake of example. I now, export the function and then use it in a test as follows:

container = {}

describe('Repository', () => {
  it('should connect with a container', () => {
    let hello = repository(container)

    expect(hello).toMatchObject({
      makeBooking: jest.fn('makeBooking'),
      getOrderById: jest.fn('getOrderById'),
      generateTicket: jest.fn('generateTicket'),
      disconnect: jest.fn('disconnect')
    })
  })
})

The Error I am getting is :

 Expected value to match object:
      {"disconnect": [Function mockConstructor], "generateTicket": [Function mockConstructor], "getOrderById": [Function mockConstructor], "makeBooking": [Function mockConstructor]}
    Received:
      {"disconnect": [Function disconnect], "generateTicket": [Function generateTicket], "getOrderById": [Function getOrderById], "makeBooking": [Function makeBooking]}

I need to mock the object being returned from the repository object. However, this object consists named functions as shown in the code. is there anyway to mock objects with functions inside them?

Answer 1

You can use jest.spyOn to make a stub for the methods of repository.

You mock or stub the methods of the repository, you need to use them. This is why the service.js come from, of course, you can use the repository anywhere. So, actually the method to be tested is service.makeBooking. Then, you can make assertion for the makeBooking method of the repository, for example, to check the mocked/stubbed makeBooking method of the repository to have been called or not.

And here we use dependency injection pattern to inject the mocked hello object to service.makeBooking(hello) method.

E.g.

repository.js:

const repository = (container) => {
  const makeBooking = (user, booking) => {
    'make booking function called';
  };

  const generateTicket = (paid, booking) => {
    console.log('generate ticket function called');
  };

  const getOrderById = (orderId) => {
    console.log('get order by ID called');
  };

  const disconnect = () => {
    console.log('disconnect method called');
  };

  return {
    makeBooking,
    getOrderById,
    generateTicket,
    disconnect,
  };
};

module.exports = repository;

repository.test.js:

const repository = require('./repository');

const container = {};

describe('Repository', () => {
  it('should connect with a container', () => {
    let hello = repository(container);

    expect(hello).toMatchObject({
      makeBooking: expect.any(Function),
      getOrderById: expect.any(Function),
      generateTicket: expect.any(Function),
      disconnect: expect.any(Function),
    });
  });

  it('should generate ticket', () => {
    let hello = repository(container);
    const logSpy = jest.spyOn(console, 'log');
    hello.generateTicket();
    expect(logSpy).toBeCalledWith('generate ticket function called');
  });

  // rest test cases same as above
});

unit test results with coverage report:

 PASS  stackoverflow/61268658/repository.test.js (11.281s)
  Repository
    ✓ should connect with a container (5ms)
    ✓ should generate ticket (19ms)

  console.log node_modules/jest-environment-enzyme/node_modules/jest-mock/build/index.js:866
    generate ticket function called

---------------|---------|----------|---------|---------|-------------------
File           | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
---------------|---------|----------|---------|---------|-------------------
All files      |      80 |      100 |      40 |      80 |                   
 repository.js |      80 |      100 |      40 |      80 | 11,15             
---------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        13.132s

service.js:

const service = {
  makeBooking(hello) {
    return hello.makeBooking();
  },
};

module.exports = service;

service.test.js:

const service = require('./service');
const repository = require('./repository');
const container = {};

describe('service', () => {
  it('should init', () => {
    let hello = repository(container);
    jest.spyOn(hello, 'makeBooking').mockReturnValueOnce('fake data');
    const actual = service.makeBooking(hello);
    expect(actual).toEqual('fake data');
    expect(hello.makeBooking).toBeCalledTimes(1);
  });
});

unit test results with coverage report:

 PASS  stackoverflow/61268658/service.test.js (10.94s)
  service
    ✓ should init (4ms)

---------------|---------|----------|---------|---------|-------------------
File           | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
---------------|---------|----------|---------|---------|-------------------
All files      |   76.92 |      100 |   33.33 |   76.92 |                   
 repository.js |      70 |      100 |      20 |      70 | 7,11,15           
 service.js    |     100 |      100 |     100 |     100 |                   
---------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        12.278s