การใช้งาน Mock ใน Jest

import { add } from '../math'

export const doubleSum = (x: number, y: number): number => {
  const sum = add(x, y)
  return x + y + sum
}

export const add = (x: number, y: number): number => x + y

import { doubleSum } from './calculate'

test('should return 6 when call doubleSum and send 1 and 2', () => {
  const numberOne = 1
  const numberTwo = 2
  // 6 = 1 + 2 + 1 + 2
  const expected = 6 

  const result = doubleSum(numberOne, numberTwo)

  expect(result).toBe(expected)

})

jest.mock('../../../src/function/math', () => ({
  add: jest.fn()
}))

import { doubleSum } from './calculate'

// Implement in Mock
jest.mock('../../../src/function/math', () => ({
  add: jest.fn().mockImplementation((x, y) => {
    if (x === 1 && y === 2) return 20

    return x + y
  })
}))

describe('Basic Mock solution 1', () => {
  afterEach(() => {
    jest.restoreAllMocks()
  })

  test('should return 23 when call doubleSum and send 1 and 2', () => {
    const numberOne = 1
    const numberTwo = 2
    // if not mock return value (1 + 2) + (1 + 2) = 6
    const expected = 23
  
    const result = doubleSum(numberOne, numberTwo)
  
    expect(result).toBe(expected)
  })
  
  test('should return 23 when call doubleSum and send 10 and 2', () => {
    const numberOne = 10
    const numberTwo = 2
    const expected = 24
  
    const result = doubleSum(numberOne, numberTwo)
  
    expect(result).toBe(expected)
  })
})

import { doubleSum } from './calculate'

// 1. Import Math.ts
import * as math from './math'

// 2. Create mock
jest.mock('../../../src/function/math')

describe('Basic Mock solution 2', () => {
  test('should return 20 when call doubleSum and send 1 and 2', () => {
    // Arrange
    const numberOne = 1
    const numberTwo = 2
    const expected = 20

    // 3. Implement Mock in it.
    const addMock = math.add as jest.Mock
    addMock.mockReturnValue(17)

    const total = doubleSum(numberOne, numberTwo)

    expect(addMock).toHaveBeenCalled()
    expect(total).toBe(expected)
  })

  test('should return 110 when call doubleSum and send 1 and 2', () => {
    // Arrange
    const numberOne = 99
    const numberTwo = 1
    const expected = 100

    // 3. Implement Mock in test
    const addMock = math.add as jest.Mock
    addMock.mockReturnValue(0)

    const total = doubleSum(numberOne, numberTwo)

    expect(addMock).toHaveBeenCalled()
    expect(total).toBe(expected)
  })
})

  afterEach(() => {
    jest.restoreAllMocks()
  })

import _ from 'lodash'

export const getUserByUserName = (keyword: string) => {
  var users = [
    { user: 'barney', birthday: '1980-01-01', age: 47 },
    { user: 'fred', birthday: '1990-01-01', age: 37 },
    { user: 'pebbles', birthday: '2000-01-01', age: 27 }
  ]

  const index = _.findIndex(users, (o) => {
    return o.user == keyword
  })

  return users[index]
}

import _ from 'lodash'
import { getUserByUserName } from './user'

// Normal without mock will throw error
// jest.mock('lodash')

describe('mock', () => {
  afterEach(() => {
    jest.restoreAllMocks()
  })

  // 1. Normal without mock
  it('Should be index from keyword without mock', () => {
    const keyword = 'barney'

    const actual = getUserByUserName(keyword)

    expect(actual).toMatchObject({
      user: 'barney',
      birthday: '1980-01-01',
      age: 47
    })
  })

  // 2. With mock
  it('Should be index from keyword with mock', () => {
    const keyword = 'barney'

    // Mock lodash
    jest.mock('lodash')
    const mockFindIndex = jest.fn().mockReturnValue(2) // pebbles
    _.findIndex = mockFindIndex // Override lodash (optional, if needed)

    const actual = getUserByUserName(keyword)

    expect(mockFindIndex).toHaveBeenCalled()
    expect(actual).toMatchObject({
      user: 'pebbles',
      birthday: '2000-01-01',
      age: 27
    })
  })
})