You can get a huge amount of confidence and coverage from integration tests that test an entire page, or even your entire app. Let’s write a test that renders our whole app using React Testing Library and navigate around it like a normal user would. These tests are typically a bit longer, but they provide a huge amount of value.

Test React Components with Jest and React Testing Library

Write React Application Integration Tests with React Testing Library

Instructor: [0:01] Here we have a simple [app](https://github.com/kentcdodds/react-testing-library-course/blob/tjs/src/app.js) that has a multipage form. We have state that's going across these pages. If I click on "Fill Out the Form," then I have my favorite food I can enter, which is enchiladas. Then we can go "Next," and that's my favorite drink -- raspberry lemonade.

[0:18] Then we'll review. We'll see my favorite food and favorite drink, and we can click on "Confirm." "Congrats, you did it." Now we can go back Home, fill out the form again for all time and all eternity. Let's go ahead and see how we can test this thing.

[0:31] Here's how it's implemented. In `app.js`, we have this `MultiPageFormProvider` so that we can access this state across these pages, and we have this `useMultiPageForm` custom hook, and then we have our `Main` screen. Fill Out the Form, then `Page1`.

[0:44] That's going to get our history from react-router. We can go to `Page2` when this form is submitted. We get that `form` value and `setFormValues` to update that form value. Then we have our links to go Home and go Next.

[0:56] `Page2` is pretty similar to before where we have our favorite drink. We can fill out our favorite drink value and then go to the review page, and then this review page we have the ability to `Confirm` the values that it's printing out to us.

[1:10] Then we have the `Success` page, and in the event of an error we'll see an error message, and it all comes together in this `App` component that uses React `<Router>` to render out these different pages.

[1:21] This is also managing our `MultiPageFormProvider` with the initial values of food and drink being emptying strains. We want to test all of this together. Let's get started. In `app-01.js`, I'm going to `import React from 'react'`. We'll `import {render, fireEvent} from '@testing-library/react'`, and we'll `import App from '../app'`.

#### app-01.js
```js
import React from 'react'
import {render, fireEvent} from '@testing-library/react'
import App from '../app'
```

[1:43] One thing that I want to make sure that we don't do with this app is make HTTP calls, and we do that on this confirm page where we call this `submitForm`. I want to mock that out, and that's coming from our `./api.js`. I'm going to say `jest.mock('../api')` so we don't make real HTTP calls, and then I'm going to make my `test`.

```js
jest.mock('../api')

test('', () => {

})
```

[2:02] This is going to say it `'Can fill out a form across multiple pages'`. I know this is going to be `async` test, so I'll just add `async` there right now. I also know that `submitForm` is going to be called, so I'm going to import `submitForm`, and I'll alias that to mock `submitForm` from our api.

```js
import React from 'react'
import {render, fireEvent} from '@testing-library/react'
import {submitForm as mockSubmitForm} from '../api'
import App from '../app'

jest.mock('../api')

test('Can fill out a form across multiple pages', async () => {

})
```

[2:21] Right from the get-go I'm going to say `mockSubmitForm`, `mockResolveValueOnce`, `success: true` so what our server would send back if we were to hit the API directly. Then let's go ahead and make some `testData`. We'll have our food test food and our drink will be our test drink, and then let's `render` this app.

```js
test('Can fill out a form across multiple pages', async () => {
  mockSubmitForm.mockResolveValueOnce({success: true})
  const testDAta = {food: 'test food', drink: 'test drink'}
  render(<App />)
})
```

[2:43] We know we're going to need to `getByLabelText` so we can fill out that form. We'll also need `getByText` so we can click on some buttons. Let's pull out `debug` so that we can follow along as we go.

```js
const {getByLabelText, getByText, debug} = render(<App />)

debug()
```

[2:55] I'll save that, open this up. Here we are on the home screen. Let's click on fill out the form. We'll say `fireEvent.click(getByText())`. Let's make this a pretty generous regex, so `fill.*form` ignore case. If we change it to fill out the form or fill the form out, or whatever we change it to, that should find the text and it should work pretty well. 

```js
fireEvent.click(getByText(/fill.*form/i))
```

We'll click on that.

[3:19] We move on to that next page. Here we are with the favorite food. Let's fill that out by saying `fireEvents.change(getByLabelText(/food/))` ignore case. We're going to say the `target` for this change event should have a `value` that is sent to our `testData.food`. 

```js
fireEvents.change(getByLabelText(/food/i), {target: {value: testData.food}})
```

Set that. There we go, our test data food. Perfect.

[3:40] Now, we're going to move on to the next page by `fireEvent.click(getByText)`. What does it say? Next? We'll say `next`. 

```js
fireEvent.click(getByText(/next/i))
```

We'll save that. Now we're on the favorite drink page.

[3:51] We'll do something pretty similar to the last page. This will be by labeled text `drink`. The value for this one will be `testEata.drink`. On this page, we don't have a next button. That's why that's failing. We'll have a `review` button. Let's update `next` to `review`. 

```js
fireEvents.change(getByLabelText(/drink/i), {target: {value: testData.drink}})
fireEvent.click(getByText(/review/i))
```

Save that.

[4:08] Now we're on the confirmation page. Let's verify that the `span` that is label by the food label, so favorite food. Get by label favorite food, get by label favorite drink, and we'll verify that those values are correct.

[4:24] We can `expect`, `getByLabelText`, `food,` `toHaveTextContent`, `testData.food`. 

```js
expect(getByLabelText(/food/i)).toHaveTextContent(testData.food)
```

Save that.Our test is still passing. We'll do the same thing for our drink, test-data.drink. 

```js
expect(getByLabelText(/drink/i)).toHaveTextContent(testData.drink)
```

We're good.

[4:39] Now, we can `fireEvent.click()` on the confirmation button, `getByText`, `confirm`. 

```js
fireEvent.click(getByText(/confirm/i))
```

We'll click on that. We should be on the next page.

[4:52] Oh, but we're getting multiple elements with the text confirm. That is not intentional. We're not going to use the all by variants of the query. It looks confirm is showing up in this H2 as well as our button. That's pretty common.

[5:05] What we're going to do here is we'll just say `selector: button`. We'll scope this get by text to only those elements that match the CSS selector button. 

```js
fireEvent.click(getByText(/confirm/i, {selector: 'button'}))
```

We'll save that. Now we have clicked on confirm, but we're not moving on to the next page. Why is that?

[5:20] Let's take a look at what happens when we click on that button in `app.js`. We're going to come down here to our `Confirm` component, and when we click on Confirm, we're going to submit the form. That's going to be an asynchronous operation.

[5:31] The next thing that we're looking for is the home link that's on the success page. Let's choose to do some asynchronous waiting for that link to show up. To do that, we're going to bring in `findByText` back in `app-01.js`. We'll come down here and we'll `await findByText`, `home`, to find that home link, we'll save that.

```js
const {getByLabelText, getByText, debug, findByText} = render(<App />)

...

await findByText(/home/i)
```

[5:49] Now, after that mock request has been made, we get this, "Congrats, you did it!" and now we have that "Go home" link. Let's go ahead and fire an event on that. Let's say, `fireEvent.click`, and that should take us to "Welcome home" again. Then we can just say, getByText('Welcome home') and that's just as good as an assertion for us.

```js
fireEvent.click(await findByText(/home/i))

getByText(/welcome home/i)
```

[6:10] If we want to make it look a little bit more like an assertion, then we can just say, `expect`, `toBeInTheDocument()`. 

```js
expect(getByText(/welcome home/i)).toBeInTheDocument()
```

There we go.

[6:18] Now, because we're mocking out this request, let's just make sure it's being called properly. We'll get rid of `debug`. We'll come down here, right where it's being called, and we'll, `expect(mockSubmitForm).toHaveBeenCalledWith()`, and let's see what it's called with. Looks like, Drink and Test Foods.

[6:36] That's just our test data, so I'll save that. We've got that passing. Let's make sure it's only called once. We don't want it to be called more than one time. 

```js
const {getByLabelText, getByText, findByText} = render(<App />)

...

expect(mockSubmitForm).toHaveBeenCalledWith(testData)
expect(mockSubmitForm).toHaveBeenCalledTime(1)
```

Good, we've got a really good test here for this entire application.

[6:50] We're not mocking out a whole lot. We're testing our React router, we're testing navigating between pages, we're testing our state provider. All of that is happening just by rendering this app and interacting with our app in the same way our end user would.

[7:04] The only things that we are mocking out are API calls. We don't actually make API calls to the back-end server during our tests. That's something you'd reserve for end-to-end tests.

[7:14] Here, we start out, we click on Fill Out the Form, we fill out the Food value, then click on Next. We fill out the Drink value, click on review. We make sure that the review data is what it should be. We click on Confirm, we make sure our mockSubmitForm is being called properly.

[7:28] We wait for the home link to show up, and when it does, we click on it, and then we verify that we have made it to the home page. This gives us a ton of confidence in a pretty reasonable test.


If you want to ship your applications with confidence - and of course you do - you need an excellent suite of automated tests to make absolutely sure that when changes reach your users, nothing gets broken. To get this confidence, your tests need to realistically mimic how users actually use your React components. Otherwise, tests could pass when the application is broken in the real world.

In this course, we’ll write a series of render methods and run a range of tests to see how we can get the confidence we’re looking for, without giving up maintainability or test run-speed.

What's changed in Test React Components with Jest and React Testing Library

Intro to Test React Components with Jest and React Testing Library

Let’s start basic by using ReactDOM to render a simple React component to a <div> we create ourselves and assert that it’s rendering the right thing based on the props we provide.

Render a React Component for Testing

The Jest DOM library provides really useful extensions to jest’s built-in assertion library that will make it easier for us to write our test assertions (like toHaveTextContent). Let’s see how to use that in our project.

Use Jest DOM for Improved Assertions

Our tests are currently tightly coupled to the implementation of our component’s element structure. A refactor to that structure wont break our application, but will definitely break our tests because we’re testing implementation details. Let’s use DOM Testing Library to create a custom render function that will give us some helpful utilities for searching for elements in the DOM in the same way a user would.

Use DOM Testing Library to Write More Maintainable React Tests

Let’s create a simple render method to be able to reuse this functionality for our other tests. The render method we’ve created is similar to [the render method](https://testing-library.com/docs/react-testing-library/api#render) that’s provided by React Testing Library. Let’s swap our implementation to that!

Use React Testing Library to Render and Test React Components

While you’re writing your tests it can be helpful to see what the DOM looks like. You can do this with React Testing Library’s debug function which will log a formatted and syntax highlighted state of the DOM at the time it is called.

Debug the DOM State During Tests using React Testing Library’s debug Function

The fireEvent utility in React Testing Library supports all the events that you regularly use in the web (change, click, etc.). Let’s see how we can test our change event handler with an input.

Test React Component Event Handlers with fireEvent from React Testing Library

The User Event module is part of the Testing Library family of tools and lets you fire events on DOM nodes that more closely resemble the way your users will interact with your elements. Let’s refactor our fire event usages to use that instead.

Improve Test Confidence with the User Event Module

Sometimes it can be useful to change the props of a component you’ve rendered and make assertions about what’s rendered after that prop change has taken place. Let’s see how to go about doing this with React Testing Library.

Test Prop Updates with React Testing Library

It’s pretty straightforward to assert that a certain element is rendered with react-testing-library, but what if we want to ensure that something is NOT being rendered. For example, if we re-render our component with a different maximum amount leading to the error message being hidden. Let’s see how we can use the query* APIs from react-testing-library to assert that certain elements are not rendered.

Assert That Something is NOT Rendered with React Testing Library

While not all of accessibility testing of a web application can be automated, much of it can be and quite easily using [axe-core](https://github.com/dequelabs/axe-core) and [jest-axe](https://github.com/nickcolley/jest-axe). Let’s see how to integrate this with React Testing Library to help catch common accessibility issues.

Test Accessibility of Rendered React Components with jest-axe

If you have a component that makes HTTP requests, you’ll probably want to mock those out for UI unit and integration tests. Let’s see how to use jest’s built-in mocking capabilities to do that.

Mock HTTP Requests with jest.mock in React Component Tests

Mocking an API module works, but it's incomplete because we have to make all these assertions that we're calling it properly and then we'd need to write some other tests for the API module itself to make sure that it responds properly to those calls. 

In this lesson, I'll show you how you can use a package called [MSW](https://mswjs.io/) to intercept and handle those HTTP requests instead so we can get a great deal more confidence.

[Get the code on GitHub](https://github.com/kentcdodds/react-testing-library-course/blob/46d2608caaa404476c9224cd136aea270a739e6d/src/__tests__/http-msw-mock.js)

Mock HTTP Requests with MSW

There are some situations where you want to focus your tests on a particular component and not any of its children. There are other situations where you want to mock out the behavior of components that your component renders. In the case of react-transition-group, we don’t want to have to wait until the transition has completed before we can go on with our tests. Let’s see how we can mock the implementation of react-transition-group using jest.mock to make our tests more reliable and easier to write and maintain.

Mock react-transition-group in React Component Tests with jest.mock

If the user experiences an error while using your application you may want to send information to a monitoring tool to ensure you can be made aware of the error and deal with it as quickly as possible. Let’s see about testing a component that is responsible for this componentDidCatch error boundary using React Testing Library.

Test componentDidCatch Handler Error Boundaries with React Testing Library

When testing an error boundary, your console will be filled with console.error calls from React. Those can be a real distraction from the rest of the output for your tests. Let’s clean those up with jest.spyOn.

Hide console.error Logs when Testing Error Boundaries with jest.spyOn

Our error boundary has some other use cases that it supports and we should try to make sure our tests cover all those use cases, so let’s add a test to make sure the recovery feature of our error boundary works properly.

Ensure Error Boundaries Can Successfully Recover from Errors

We have a bit of repetition in our rerender calls here and it would be nice if we could avoid that. Let’s use the wrapper option for React Testing Library so we can avoid the repetition in our rerender calls.

Use React Testing Library’s Wrapper Option to Simplify using rerender

Normally using Test Driven Development (TDD) with UI is really difficult because testing utilities for UI often tie your tests closely to the implementation. Because React Testing Library is not this way, we can actually use it to TDD our UI. Let’s build the structure of a form using TDD with React Testing Library.

Test Drive the Development of a React Form with React Testing Library

Now that we have our react form structure written using TDD, let’s take it a step further and TDD our form’s submission with an onSubmit handler as well.

Test Drive the Submission of a React Form with React Testing Library

Once the data has been saved on the server, we’ll want to redirect the user to the home screen with react-router’s <Redirect /> component. Let’s go ahead and mock that component as well and verify that it’s being rendered with the correct props. We’ll have to make our test asynchronous so we can make that assertion because the <Redirect /> component is rendered after the async call happens.

Test Drive Mocking react-router’s Redirect Component on a Form Submission

It’s great that our form can be submitted, but we need to get that data to our server to actually save the post to the database. We don’t want to actually make requests to the server during these unit tests, so we’ll mock out the function responsible for doing that and assert that it’s being called with the right data. Then we’ll go ahead and implement that functionality in our form component.

Test Drive the API Call of a React Form with React Testing Library

Our post should probably have a creation date associated with it (typically you’ll add this on the server, but for the purposes of our example, we’ll do it on the client). Dates are notoriously challenging to test. There are existing libraries that help, but often you can get close enough to the desired effect for your assertions. Let’s go ahead and test that a correct creation date has been set for our posts.

Test Drive Assertions with Dates in React

A really important aspect of TDD is the refactor phase. A critical piece to making your tests easier to maintain is using code structure and values to communicate what is important and what is not. We’ll use data generation with [test-data-bot](https://github.com/jackfranklin/test-data-bot) to communicate that the specific data values are irrelevant and it’s just what kind of data it is. Let’s refactor our tests to communicate this effectively.

Use Generated Data in Tests with tests-data-bot to Improve Test Maintainability

We have the happy path covered for our post editor component, but what happens if there’s an error in saving the user’s information? We should probably show them an error message and give them the chance to try again. Let’s add a new test for this error case and implement some error handling.

Test Drive Error State with React Testing Library

We’ve finished with our post editor component, but let’s not forget the refactor phase! We have a bunch of duplicate logic between our two tests. When you have multiple tests with duplicate logic, it becomes hard for folks who come to maintain the tests later to identify what the differences between the tests are. This makes it harder to understand what the different features of the component are. So let’s refactor the tests slightly so we can communicate clearly what the important and unique parts of the tests are to make it easier for future maintainers.

Write a Custom Render Function to Share Code between Tests and Simplify Tests

Mocking the <Redirect /> component in react-router works, but it’s imperfect because we don’t know for sure that the user will be redirected properly. Alternatively, we can render our component within a Router with a custom implementation of a history via createMemoryHistory. Then we can make assertions on that history object.

Test React Components that Use the react-router Router Provider with createMemoryHistory

If the user enters a bad URL or there’s some kind of routing error, we should show the user a helpful error page. Let’s see how we can test that our page is wired up with the router properly to do this.

Initialize the `history` Object with a Bad Entry to Test the react-router no-match Route

Many of our components need (or will eventually need) the router context from the router provider. Let’s write a custom render method that looks and acts like the render method from React Testing Library but adds features for our router so we don’t have to concern ourselves about the implementation detail of the router.

Create a Custom render Function to Simplify Tests of react-router Components

Similar to react-router, we can render our component under test with the redux provider, our full redux store, and then we can interact with our component in the same way the user would and be confident that our component, action creators, and reducers are all working properly.

Test a Redux Connected React Component

There are definitely some scenarios where you want to test what a component will do given certain state in the store. Let’s see how we can initialize our redux provider with a store that has some custom initialized data. One thing that I should note here is that while it can be useful to do this, make sure you at least have one test that verifies that you can  into this state in the first place.

Test a Redux Connected React Component with Initialized State

It’s very common for our components to use state from the redux store (or to be refactored to use it eventually). Having to change our tests every time we do this would be frustrating. Let’s see how we can write a render method we could use to not worry about that implementation detail when it’s irrelevant for our tests. This could be combined with the custom render method for the router to be a single render method that supports all providers our components need.

Create a Custom Render Function to Simplify Tests of Redux Components

We’ve got a custom useCounter hook here and we want to make sure the increment and decrement functions it returns will update the count state that it returns. Because hooks must be run within the render phase of a component, we’ll create a simple component that simply uses the hook and render that component. One catch is that whenever there’s a state update in your tests, React needs you to wrap that in a call to act. We don’t have to do that for regular component tests that use React Testing Library utilities because those utilities manage the act call internally, but since we’re calling these state updater functions ourselves, we have to wrap things in act. Let’s do that for our useCounter hook.

Test a Custom React Hook with React’s Act Utility and a Test Component

Once we add tests for all the use cases of our hook, we’ll notice a bunch of common setup, so let’s put that in a setup function.

Write a Setup Function to Reduce Duplication of Testing Custom React Hooks

That setup function is pretty handy. Seems like a good opportunity for an abstraction. Well, we already have one! It’s called React Hooks Testing Library. Let’s swap our setup function for the renderHook function from @testing-library/react-hooks.

Test a Custom React Hook with renderHook from React Hooks Testing Library

Just like React Testing Library, React Hooks Testing Library has a rerender function which can be useful for testing changes to props. Let’s test what happens if the step option changes for our hook.

Test Updates to Your Custom React Hook with rerender from React Hooks Testing Library

When you use a React Portal, much of your component can be rendered outside the main DOM tree. Let’s see how we can use utilities provided by React Testing Library to allow us to select elements within the portal. To perform actions and assert on what’s rendered.

Test React Portals with within from React Testing Library

Sometimes your react component may need to do some cleanup work in the return value from useEffect or useLayoutEffect, or the componentWillUnmount lifecycle method for class components. Luckily for us, as far as React Testing Library is concerned, whichever of those you use is an implementation detail, so your test looks exactly the same regardless of how you implement it. Check out how you can test that simply with React Testing Library and a <Countdown /> component.

Test Unmounting a React Component with React Testing Library

By using some of the get* queries, we’re assuming that those elements will be available on the page right when we execute the query. This is a bit of an implementation detail and it’d be cool if we could not make that assumption in our test. Let’s swap all those for find* queries.

Improve Reliability of Integration Tests using find* Queries from React Testing Library

Let’s take things a step closer to the way our app is used by using the User Event module for interacting with our app. Once we’ve done all this implementation detail-free testing, we’ll find out that we can drastically change the implementation of our app and our tests can give us confidence that our changes were successful. That’s fantastic!

Write React Application Integration Tests with React Testing Library

Transcript

Write React Application Integration Tests with React Testing Library