What benefits can be gained from utilizing the beforeEach function within Jest testing?

Question

What benefits can be gained from utilizing the beforeEach function within Jest testing?

I am currently immersing myself in the world of Jest by following this informative guide. Can you explain the benefits of utilizing the beforeEach function in Jest?

I have a particular interest in identifying action dispatches. I believe that two segments of code below will yield identical outcomes.

describe('dispatch actions', () => {
  const localVue = createLocalVue()
  localVue.use(Vuex)

  let actions = { increment: jest.fn(), decrement: jest.fn() }
  let store = new Vuex.Store({ state: {}, actions })

  const wrapper = shallowMount(Counter, { store, localVue })

  it('calls "increment" when plus button is clicked', () => {
    wrapper.find('button#plus-btn').trigger('click')
    expect(actions.increment).toHaveBeenCalled()
  })

  it('calls "decrement" when minus button is clicked', () => {
    wrapper.find('button#minus-btn').trigger('click')
    expect(actions.decrement).toHaveBeenCalled()
  })
})

describe('dispatch actions', () => {
  const localVue = createLocalVue()
  localVue.use(Vuex)

  let actions
  let store

  beforeEach(() => {
    actions = {
      increment: jest.fn(),
      decrement: jest.fn()
    }
    store = new Vuex.Store({
      state: {},
      actions
    })
  })

  it('triggers "increment" upon clicking the plus button', () => {
    const wrapper = shallowMount(Counter, { store, localVue })
    wrapper.find('button#plus-btn').trigger('click')
    expect(actions.increment).toHaveBeenCalled()
  })

  it('triggers "decrement" upon clicking the minus button', () => {
    const wrapper = shallowMount(Counter, { store, localVue })
    wrapper.find('button#minus-btn').trigger('click')
    expect(actions.decrement).toHaveBeenCalled()
  })
})

javascript vue.js jestjs

Answer 1

Answer №1

These examples showcase different behaviors. According to the Jest documentation (https://jestjs.io/docs/en/setup-teardown), the beforeEach method is executed before each test method.

In the first example, the action and store are created only once, so changes made in the first test method (increment) persist for the second test. Conversely, the second example recreates the action and store for each test, resulting in changes not carrying over between tests.

Typically, the second approach is preferred as it allows for independent tests with no shared state, which is considered a good practice.

Answer 2

These examples showcase different behaviors. According to the Jest documentation (https://jestjs.io/docs/en/setup-teardown), the beforeEach method is executed before each test method.

In the first example, the action and store are created only once, so changes made in the first test method (increment) persist for the second test. Conversely, the second example recreates the action and store for each test, resulting in changes not carrying over between tests.

Typically, the second approach is preferred as it allows for independent tests with no shared state, which is considered a good practice.

Answer 3

Answer №2

It has been previously stated that the function beforeEach is executed before each test.

Another important benefit of using both beforeAll and beforeEach is that you can provide them with either a function that returns a Promise or an async function, allowing Jest to wait for the resolution of the resulting Promise before proceeding.

Therefore, it is crucial to use beforeAll and beforeEach for any asynchronous setup tasks:

describe('something', () => {

  let setInBeforeAll, setinBeforeEach;

  beforeAll(() => {
    return returnsAPromise().then(val => {  
      setInBeforeAll = val;
    });
  });

  beforeEach(async () => { 
    setInBeforeEach = await alsoReturnsAPromise();
  });

  it('should do something', () => {
    // both setInBeforeAll and setInBeforeEach are accessible here
  });
});

Answer 4

It has been previously stated that the function beforeEach is executed before each test.

Another important benefit of using both beforeAll and beforeEach is that you can provide them with either a function that returns a Promise or an async function, allowing Jest to wait for the resolution of the resulting Promise before proceeding.

Therefore, it is crucial to use beforeAll and beforeEach for any asynchronous setup tasks:

describe('something', () => {

  let setInBeforeAll, setinBeforeEach;

  beforeAll(() => {
    return returnsAPromise().then(val => {  
      setInBeforeAll = val;
    });
  });

  beforeEach(async () => { 
    setInBeforeEach = await alsoReturnsAPromise();
  });

  it('should do something', () => {
    // both setInBeforeAll and setInBeforeEach are accessible here
  });
});

What benefits can be gained from utilizing the beforeEach function within Jest testing?

Answer №1

Answer №2

Similar questions

Strategies for sending data to child components in Vue

Is there a feature in JavaScript that allows for the creation of URLs?

Techniques for dynamically counting rows in a table using JavaScript

Create an animation effect where a div increases in height, causing the divs beneath it to shift downward in a

What is the correct way to interpret the URL of attachments in messages?

Ways to store data in the localStorage directly from a server

Parsing JSON data into different data types in C#

Ways to retrieve a concealed DOM element from a background window

Is your AngularJS code throwing an error?

Discover the steps to convert an image to base64 while circumventing the restrictions of the same-origin policy

Guide for setting up a React infinite scroll feature in a messaging app similar to Facebook Messenger

Guide to animating the height of a div using jQuery:

Show the error messages directly beneath each field

Make sure your test suite includes a minimum of one test

What Occurs to Processed Messages in Azure Functions if Result is Not Output?

iOS is causing issues with the JavaScript function and not allowing it to

What's the best approach for revalidating data with mutate in SWR?

Using React Native's stylesheet to apply multiple values in a CSS statement

jquery-powered scrollable content container

Utilize an AJAX call to fetch an array and incorporate it within your JavaScript code