sahilrajput.com

Jest and expect

Quick Links:

Jest Cheatsheet: Click here
react testing: Click here

Bare setup with just `expect` and typescript setup:

mkdir my-jest-app; cd my-jest-app; npm init -y; mkdir __tests__ && echo "test('simple', () => expect(1).toBe(1))" > __tests__/a.ts && npm i -D expect jest @types/jest
Add script to package.json file: "test": "jest --watchAll"
Now you can run below command to start testing without even jest: npm run test
IMPORTANT: For typescript support: docs, you need to install deps: npm i -D ts-jest @babel/preset-env @babel/preset-typescript and create a file in root project i.e, babel.config.js with below contents:
```
module.exports = {
    presets: [
      ['@babel/preset-env', {targets: {node: 'current'}}],
      '@babel/preset-typescript',
    ],
  };
```

Remove default console.log format of jest

Check this issue on jest’s github: Click here

more assertion helpers for `.toEqual`

My Luxon Notes: Learn Luxon: Click here

// For services:
expect(...).toEqual({
	_id: expect.any(mongoose.Types.ObjectId),
	createdAt: expect.any(Date),
	updatedAt: expect.any(Date),
})

// For e2e:
expect(...).toEqual({
	_id: expect.stringMatching(SIMPLE_MONGODB_ID_REGEX),
	createdAt: expect.any(String),
	updatedAt: expect.any(String),
	startDate: '2022-10-24T00:00:00.000Z', // using dates with `luxon.DateTime.fromISO('2022-10-17T00:00:00Z').toJSDate().toISOString()`
	endDate: '2022-10-25T23:59:59.000Z', // using dates with `luxon.DateTime.fromISO('2022-10-25T23:59:59Z').toJSDate().toISOString()`
	// NOTE the difference of extra .000 before Z
})

File deletion and exists check with jest

it.only('if given path is exists then it will return that same path', async () => {
  function runTest() {
    const tempFilePath = path.join(os.tmpdir(), 'myfile.jpg');
    const fh = fs.openSync(tempFilePath, 'w');
    fs.writeSync(fh, '.', 3);
    fs.closeSync(fh);
    expect(existsSync(tempFilePath)).toBe(true);
    unlinkSync(tempFilePath);
    expect(existsSync(tempFilePath)).toBe(false);
  }
  for (let i = 0; i < 10_000; i += 1) {
    console.log('iter:', i);
    runTest();
  }
});

What’s the difference between “foo.spec.ts” and “foo.test.ts”?

Source: Click here

How to check multiple arguments on multiple calls for jest spies

Source: Click here

1/2 mock

Source (Jest Docs): Click here

const myMockFn = jest
  .fn(() => 'default')
  .mockImplementationOnce(() => 'first call')
  .mockImplementationOnce(() => 'second call');

console.log(myMockFn(), myMockFn(), myMockFn(), myMockFn());
// > 'first call', 'second call', 'default', 'default'

Learn about mock functions and using `jest.spyOn(..., ...).mockImplementation(() => Promise.resolve(undefined))` along with `toHaveBeenCalledWith` assertions

(check: Why use mock testing functions in telegram slasher-private-channel to know specifics learned)

Medium Article suggested by Eric’s Suggested Article: Click here

For bettter testing use `expect().toEqual(...)`

Tip: If you don’t have string matches you can use store sample date in .json file as well.

```js import expect from ‘expect’

const SIMPLE_MONGODB_ID_REGEX = /^[a-f\d]{24}$/i // 24 characters ~Sahil

const response = [
	{
		_id: '63ab12b2fa6c5356d22a298d',
		userName: 'yolo',
		firstName: 'Nelson Mandela',
		profilePic: 'http://localhost:4444/placeholders/default_user_icon.png',
	},
]

// Learn Usage of:
// 1. .toEqual(...)
// 2. expect.stringMatching(...)
// 3. expect.not.stringContaining(...)

expect(response).toEqual([
	{
		_id: expect.stringMatching(SIMPLE_MONGODB_ID_REGEX),
		userName: 'yolo',
		firstName: 'Nelson Mandela',
		profilePic: 'http://localhost:4444/placeholders/default_user_icon.png',
	},
])
expect([{name: 'sahil rajput'}]).toEqual([
	{
		name: expect.stringContaining('sahil'),
	},
])
expect([{name: 'sahil rajput'}]).toEqual([
	{
		name: expect.stringContaining('rajput'),
	},
])
expect([{name: 'sahil rajput'}]).toEqual([
	{
		name: expect.not.stringContaining('om'),
	},
])
  	```

Testing asynch operation with jest

  describe.only('something', () => {
    it.only('shoudl it be?', (done) => {
      console.log('hello');
      done() // if done is not called then the test will not pass at all. In fact the setTimeout warning is thrown.
    });
  });

Socket.io Testing with jest:

Click here: Official Docs - Click here

Amazingly defined funcion to wait for a callback function but reject after 2 seconds if didn’t receive the event, YO!!

Jest debugging command from official docs:

node --inspect-brk node_modules/.bin/jest --runInBand [any other arguments here]

Define test timeout for a individual test like that

  it('does a lot of stuff exceeding default 5 sec timeout', async () => {
    // ...
  }, 10000)