Unit Testing

React + Redux Applications

Nikhil John

Sprinkle .test.js files directly next to the parts of your application you want to test. (Or in test/ subdirectories, it doesn't really matter as long as they are directly next to those parts and end in .test.js)
Write your unit tests in those files.
```
npm run test:watch
OR
```
```
npm run test
```

Jest test framework runs tests and make assertions.
Writing tests ~ speaking - you describe a unit of your code and expect it to do the correct thing

// add.js

export function add(x, y) {
  return x + y;
}

// add.test.js
import { add } from '../add';
describe ('add()', () => {
  it('adds two numbers', () => {

    expect(add(1, 2)).toEqual(5);
  });
  it('doesn't add subsequent args after second', () => {

    expect(add(1, 2, 3)).toEqual(add(1,2));
  });
})

Should our function work, Jest will show this output when running the tests:

add()
  ✓ adds two numbers
  ✓ doesn't add subsequent args after second

// add.js

export function add(x, y) {
  return x * y;
}

add() › adds two numbers

  expect(received).toEqual(expected)

  Expected value to equal:
    5
  Received:
    6

add()
  ✕ adds two numbers

  ✓ doesn't add the third number