jest mock debug.js module

foo.test.js

/* eslint-env jest */

const mockDebug = jest.fn()
jest.mock('debug', () => {
  return () => mockDebug
})
const foo = require('./foo')

describe('foo.bar', () => {
  it('should testName', () => {
    mockDebug.mockClear()
    mockDebug.mockReset()
    foo.bar()
    expect(mockDebug).toBeCalled()
    expect(mockDebug.mock.calls).toMatchSnapshot()
  })
})

jest-mock-debug.js

const debug = require('debug')('foo')

function bar () {
  debug('hello world')
}

module.exports = {
  bar
}

exmaple: typescript + jest + mock debug.js module

declare global {
  var mockDebug: jest.Mock<any, any>;
}

jest.mock('debug', () => {
  global.mockDebug = jest.fn();
  return () => global.mockDebug;
});

// usage
describe('xxx', () => {
	test('xxx', () => {
		expect(global.mockDebug.mock.calls.toString()).toContain('ccc');
	})
});