https://github.com/tsmx/jest-process-exit

Testing process.exit with Jest in NodeJS
https://github.com/tsmx/jest-process-exit

exit jest nodejs process testing

Last synced: 2 months ago
JSON representation

Testing process.exit with Jest in NodeJS

• Host: GitHub
• URL: https://github.com/tsmx/jest-process-exit
• Owner: tsmx
• License: mit
• Created: 2020-08-07T11:07:38.000Z (over 4 years ago)
• Default Branch: master
• Last Pushed: 2024-06-18T19:10:10.000Z (7 months ago)
• Last Synced: 2024-06-19T00:51:33.806Z (7 months ago)
• Topics: exit, jest, nodejs, process, testing
• Language: JavaScript
• Homepage:
• Size: 575 KB
• Stars: 3
• Watchers: 2
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

README

        
# Testing process.exit with Jest in NodeJS

## The scenario

Consider you have the following function to be tested with [Jest](https://jestjs.io/):

```javascript

function myFunc() {

    //

    // ...do "stuff"

    //

    if (condition) {

        process.exit(ERROR_CODE);

    }

    //

    // ...do "other stuff"

    //

 }

```

## Setting up the test case

To test the branch where `condition` is `true` you have to mock `process.exit` because otherwise the Jest test process would truly exit and therefore fail. Of course this mocking should have been done in a way that "other stuff" is never executed in this test.

To achieve that we use Jest's `spyOn` to implement a mock for `process.exit` that instead of exiting the process will throw en error.

```javascript

const mockExit = jest.spyOn(process, 'exit')

    .mockImplementation((number) => { throw new Error('process.exit: ' + number); });

```

This ensures that the execution of our function ends immediately without doing "other stuff" and without ending the Jest test process. Also this mock serves to check if `process.exit` really was called and what the exit code was. We do this with Jest's `toHaveBeenCalledWith` test function.

To get the test case up and running we have to wrap our functions execution in an `expect( ... ).toThrow()` statement because it is now throwing an error by using the mock. Also it is a good practice to restore the original mocked function by calling `mockRestore` to avoid unintended side-effects.

So we have our final test case looking like that:

```javascript

it('tests myFunc with process.exit', async () => {

    const mockExit = jest.spyOn(process, 'exit')

        .mockImplementation((number) => { throw new Error('process.exit: ' + number); });

    expect(() => {

        myFunc(true);

    }).toThrow();

    expect(mockExit).toHaveBeenCalledWith(-1);

    mockExit.mockRestore();

});

```

## Try it out

```

npm install

npm run test

```

Happy testing ;)