Jest Mock

auth.test.js

import { login, authenticate } from './auth';

jest.mock('./auth');

test('can add', () => {
  expect(2 + 2).toBe(4)
});

test('function mock', () => {
  const mockFn = jest.fn(() => 42);

  expect(mockFn()).toBe(42);

  expect(mockFn.mock.calls.length).toBe(1);
});

test('function mock with multiple returns', () => {
  const mockFn = jest.fn();

  mockFn.mockReturnValueOnce(32).mockReturnValueOnce(64);

  expect(mockFn()).toBe(32);
  expect(mockFn()).toBe(64);

  expect(mockFn.mock.calls.length).toBe(2);
});

test('auth.login mock', () => {
  login();
  expect(login.mock.calls.length).toBe(1);
});

test('auth.authenticate mock', () => {
  authenticate.mockReturnValueOnce(true);
  expect(authenticate()).toBe(true);
});

test('auth.authenticate mock false', () => {
  authenticate.mockReturnValueOnce(false);
  expect(authenticate()).toBe(false);
});