Jest mocks

jest-mocks-examples.js

// Show how to setup and create a simple Jest manual mocks

// Beginning of the example... custom.test.js

// Assume your Custom ES module and import it
import Custom from './Custom';

// Has to be after it is imported, use the file path where the module is located
jest.mock('./Custom', () => {
  const mockMethod1= jest.fn()
  const mockMethod2 = jest.fn()
  return jest.fn().mockImplementation(() => {
    return {
      method1: mockMethod1,
      method2: mockMethod2
    }
  })
})

beforeEach(() => {
 // do .mockClear() to reset mocks
})

test('some test case', () => {
  // Initialize the obj
  const cus = new Custom()
  
  // override the mock method's the return value
  cus.method1.mockReturnValue('hi')
  
  // override the implementation
  cus.method2.mockImplementation( () => {
    return 'override'
  })
})

// Mocking export function
// Original implementation: singleEntity.js
export default singleEntity(ref, fan) {
  if (ref === 'some') {
    fan.someOne()
  }
}

// Mocked
const singleEntityRenamed = require('singleEntity')
singleEntityRenamed.singleEntity = jest.fn()