Which is Jest way for restoring mocked function

Question

In Sinon's stub it is very easy to restore functionality.

const stub = sinon.stub(fs,"writeFile",()=>{})
...
fs.writeFile.restore()

I am looking to do the same thing with Jest. The closest I get is this ugly code:

const fsWriteFileHolder = fs.writeFile
fs.writeFile = jest.fn()
...
fs.writeFile = fsWriteFileHolder 

Answer 1

Finally I found a workable solution thanks to @nbkhope's contribution.

So the following code work as expected, i.e. it mocks the code and then it restore the original behavior:

const spy = jest.spyOn(
    fs,
    'writeFile' 
  ).mockImplementation((filePath,data) => {
  ...
})
...
spy.mockRestore()

Answer 2

If you want to clear all the calls to the mock function, you can use:

const myMock = jest.fn();
// ...
myMock.mockClear();

To clear everything stored in the mock, try instead:

myMock.mockReset();

Answer 3

jest.spyOn() is helpful when mocking and unmocking methods, however there might be a situation where you want to mock and unmock esModule.

I had such situation recently and I found this solution to work for me:

// Module that will be mocked and unmocked
import exampleModule from 'modules/exampleModule';

const ActualExampleModule = jest.requireActual('modules/exampleModule');

describe('Some tests that require mocked module', () => {
  // Tests on mock
});

describe('Some tests that require original module', () => {
  it('Test with restored module', async () => {
    const restoredModule = await import('modules/exampleModule');
    restoredModule.default = ActualExampleModule .default;

    // Now we can assert on original module
  });
});