Learn how to test React components by focusing on user interactions and selecting elements in an accessible way.

Queries

[00:00] Our happy path test case is passing. But when we're testing components that involve network, we need to make sure to also test different network-related scenarios, like unexpected responses, error responses, or any other business logic-defined scenarios that we have in our app. Like here, we have a second test case that displays a warning when the user

[00:19] tries to apply a legacy discount code. We know when the discount code is legacy because the server responds with a JSON response that contains is legacy key set to true. So in this case, we need to intercept the same request, but handle it differently. To do that, we will use what is called the runtime request handler. First, let's grab this worker instance

[00:39] that we prepared here. And now let's attach an overwrite. We will call worker.use and provide any request handlers that should take precedence for this test. Let's define the same handler for the post request, use the same URL that we have. But in the second function, in the resolver function, let's handle this request differently.

[00:59] We will still return a mocked JSON response, but we will provide a different response structure. Let's read the request body once again here, create a code variable and read request.text. So we have the code value here. For the amount, let's provide, let's provide 10, I think that'll be okay.

[01:18] And the legacy, let's provide true. So this will make sure that in the context of this particular test case, MSW handles this matching request with a different response. This response is different from the same happy path handler that we have in handlers.ts. So what we have to do now is to write assertions around this behavior.

[01:37] So first, let's make sure that these legacy codes are still applied, which means they're visible to the user. There's a confirmation. Let's write an assertion for that. Expand the element with text, nope, with text. And this will be the text here. The discount we provided and the discount amount

[01:57] that we provided here from the response. And we want this element to be visible on the page. But there's another expectation here. When legacy discount codes are applied, there has to be a warning that lets the user know that they applied a legacy code. So let's write assertion for that too.

[02:15] And to write this expectation correctly, let's take a look how this warning is displayed in our component. Let's go to this front component and find this scenario. I think it is here. So when there is a notification to display, we have a paragraph with the role alert and the text, whichever text we basically have

[02:34] based on the response from the server. So let's select this element as well. Expect element page get by role alert. And since it's a paragraph, it doesn't have an accessible name. So instead, we will count that there is a single alert on the page and just assert that it has a text content

[02:52] that equals the warning message that we expect. So in this case, it's this message. So what we did here, we applied a request handler overwrite that handles this request with a different response. This allows us to tap into different logical branch for testing this component and expect that the legacy codes are applied,

[03:12] but also that the warning is displayed for the user. And in a very similar manner, let's complete another test case for an error. Basically, we need to make sure that our component is able to handle network errors when applying the discount code fails. Just in the same way, let's access the worker here in the fixture, applied an overwrite worker.use,

[03:33] intercept the same request. I'm going to copy this handler. So over here, and instead of responding with a successful response, we will respond with an error response. No need to read the request body anymore. And we will just create a new response instance, provide nobody,

[03:50] and set the status code for that response to 500. So whenever this code component tries to submit the code now to this URL, it will always receive the 500 error response. And now the expectations. We need to make sure that the component actually does that handling. It will be the same handling as we did for the warning.

[04:09] So let's create another expect element, page gets by role, alerts. But now we will have a different message in that alert to have text content that will say failed to apply the discount code. So again, the principle here is the same.

[04:30] For this scenario, provide different network behavior. So component taps into that logical handling and write the expectations that in this case, we communicate to the user that applying discount has failed. Now let's try running this test. So open the terminal, run npm test, and we can see all of our three scenarios passing. And as a cherry on top,

[04:50] let me show you how can you reuse the same mocks even when developing the app. If you head to your main module, you can create a function called enable mocking where you will import this worker instance that we prepared here conditionally, for example, only when developing. And then await the worker start promise. This will start the same worker instance

[05:09] in the browser when you're developing using the same handlers you provided. And the next thing you have to do is to call this enable mocking function and defer the rendering of your app until that function resolves, until the mocking is ready. By doing this, you eliminate the race conditions between MSW activating the worker and your application potentially making requests,

[05:29] for example, on initial render. Being able to reuse the same mocks across different use cases from testing to development to debugging and showcasing your app is really powerful. And I encourage you to utilize that.

[00:00] In this exercise block, you'll be testing a new React component, and it looks like this. It's a discount code form. It consists of two elements. It's the input for the code and the button to apply it. If you want to write great component tests, you have to model them after the user. And this means finding the elements on the page the same way the user would

[00:19] and interacting with them in the same manner. In this exercise, you'll be focusing on the former. So head to a newly added test case for this form and complete it. Your task will mostly come down to two things. First is locating these elements, this input and the button in the way that's

[00:34] accessible, and then adding simple assertions that these elements are visible. Once you're done, come back to me so we can discuss this solution in more detail.

Discord

Email

GitHub

The closer your tests resemble how your software is being used, the more confidence they will give you. There’s so many great patterns stemming from this simple rule, patterns I’m sure you’re already using to write better tests.

Then, there’s the elephant in the room. **Your test environment.**

For decades, web developers have been testing their UIs in make-believe environments that are neither the browser nor Node.js. It made them come up with a frankly ridiculous amount of test setup, polyfills, and workarounds just to make it work. Remember when you had to mock `location` in tests? `window.matchMedia`? Yeah…

It’s time to abandon such practices. The tools have improved and there’s no excuse for you to be sleeping on it. It’s time for you to learn how to use Vitest Browser Mode for in-browser component testing!

## What You’ll Learn

In this workshop, you will learn a new approach to component testing that’s both different and the same. It is different because you will write and run your tests in the actual browser, taking advantage of the standard APIs and powerful browser automation. It is the same because it’s still the component level test you know and love, with rendering, querying, and asserting. 

Your users don’t interact with the UIs you build in JSDOM. They do that in the real browser, and now your tests will too!

### **Sunsetting JSDOM**

The first step in our journey is understanding why browser-like environments fall short. JSDOM has served us well, but it's time to recognize its limitations. You'll experience firsthand how browser-like environments like JSDOM are letting you down.

We'll explore examples of valid JavaScript code that works perfectly in browsers and Node.js but fails in JSDOM, undermining the value of the tests you work so hard to write. You'll discover why these inconsistencies happen and why moving to real browser testing is the solution.

### **Vitest Browser Mode**

Vitest Browser Mode allows you to run isolated component-level tests in the actual browser while providing the convenience and flexibility of integration-level testing. It's not a full end-to-end testing framework like Playwright or Cypress, but rather the perfect middle ground for component testing.

In this module, you'll learn:

- How to install and configure Vitest Browser Mode in your project;
- The technical differences between how JSDOM and Browser Mode run your tests;
- Steps needed to migrate existing JSDOM tests to Browser Mode;
- How to set up Playwright as the browser automation provider for your component tests;
- Common setup scenarios like applying global assets in tests and configuring Vitest for both unit and component-level testing within the same project.

### **Best Practices**

Choosing the right tools is important, but knowledge that transcends any particular tool is even more valuable. In this section, we'll focus on five key areas of best practices when it comes to testing your React components:

- **Queries**: Find elements on the page the same way your users or their assistive technology would;
- **User events**: Interact with the tested elements from the user’s perspective;
- **API mocking**: Use Mock Service Worker to intercept requests and handle their responses as well as discover how to efficiently use MSW in Vitest Browser Mode by creating a custom test context;
- **Element presence**: Test elements that should (or shouldn't) appear on the page reliably without false positives or flaky results.
- **Page navigation**: Learn where to draw the line when testing page transitions and routing in the actual browser.

### **Debugging Tests**

The true value of tests comes when they fail. But dealing with failing tests can be quite frustrating without the right techniques.

In this block, you'll learn some of my favorite debugging techniques that go well beyond console logging:

- How to inspect the DOM state at any point in test;
- Using the debugger statement to stop JavaScript execution entirely;
- Wielding conditional breakpoints to step through the problematic code.

These techniques will transform your approach to test failures from dread to confidence so the next time you see a failing test you will know what to do.

## Who Is This Workshop For

This workshop is for all React developers who want to write reliable and valuable tests for their components. Whether you're new to component testing or have been writing tests for years, you will inevitably learn new tools, APIs, and techniques to gain more value out of your test suite. That’s my sole motivation behind this material.

Test React components in real browsers with Vitest! Say goodbye JSDOM’s limits and catch bugs users actually face. Real tests, real results—start now!

React Component Testing with Vitest

Artem Zakharchenko

Writing tests for their own sake is a pointless chore:

```tsx
describe('add numbers', () => {
  it('should add two numbers', () => {
    expect(add(1, 2)).toBe(3)
  })

  it('should add two other numbers', () => {
    expect(add(3, 4)).toBe(7)
  })
});
```

Another annoying testing problem is when tests are too brittle, and paint your logs red even though the application seems to work just fine.

When your tests lack real purpose or seem to fail for no good reason, it's no wonder you start to question their value.

Tests are supposed to give you confidence in your code, and save you from shipping broken stuff to prod. So why does writing them feel like such a burden?

The problem is that tests like these are focused on implementation details instead of the underlying behavior. Everyone talks about the importance of testing, but there's a lack of understanding about how to write tests that are actually useful.

How would it feel to have 100% trust in your tests, knowing that any failures are not a false alarm? What if you could seamlessly translate the underlying behavior of your application into tests that are easy (and even fun) to write?

It's possible, but it requires you to take a step back from just syntax.

In order to have the confidence you're testing the right things in the right ways, you need to dig into the underlying patterns behind the scenes of a testing framework.

This is exactly what you will do in Testing Fundamentals.

In this workshop, Artem Zakharchenko, testing expert and creator of the Mock Service Worker API mocking library, will guide you through creating your own version of the Vitest testing framework.

Building a testing framework from scratch will give you a deep understanding of how the pieces fit together, and change the way you think about testing for the better.

## What You'll Learn

The workshop is broken out into four parts, each with its own challenges and exercises that build upon the last:

### Principles

First, you'll explore the principles and mental models that underlie testing strategies. This is where you will begin to distinguish between the intention of your code and its implementation details. When you focus the intention of what your code should accomplish, you can write tests that are more resilient to change.

### Test Structure

Next, you'll do a deep dive into the structure of the testing framework. You'll create your own `expect` and `test` functions, configure your test environment, and use hooks to manage side effects in your tests.

### Testing Asynchronous Code

Testing asynchronous code requires a slightly different approach when compared to testing synchronous code. Here you'll practice with testing promises and async functions, as well as handling errors and rejections.

### Moving to Vitest

Once you've learned the fundamentals of testing and built your own mini-framework, you will migrate your tests to the Vitest framework. This process will cement your understanding of not just the "hows", but also the "whys" of testing.

## Who This Workshop Is For

This workshop is for developers who have some testing experience, but feel like they're missing the bigger picture. If you're tired of writing tests that feel like a chore, and want to understand how to write tests that are actually useful, this workshop is for you.

Testing Fundamentals

Let’s face it, mocking can be really confusing.

First, you need to know what to mock. Then, find the right way to mock that thing so it doesn’t compromise your test suite. Over-mock, and your tests become pointless. Under-mock, and they get brittle instead.

In either case, you put in so much effort, and you don’t feel like you’re getting much in return.

This is where Artem comes in. He’s been proving developer misconceptions around mocking wrong for nearly a decade, and he’s here to make you a mocking pro.

## What You’ll Learn

In this hands-on workshop, you’ll learn:

- The purpose of mocking;
- What to mock and when;
- How to write mocks that bring value instead of being a maintenance chore;
- How to separate your mocks from implementation details;
- Type safety strategies for your mocks;
- And **all the mocking techniques** you will need to test your code!

By solving targeted, real-world problems using the Vitest framework, you’ll gain a comprehensive understanding of mocking and finally unlock it as a useful tool in your testing arsenal.

## Workshop Structure

This workshop contains 6 exercise blocks dedicated to various techniques on mocking different data types.

### Boundaries

Understand what mocking really is, and learn how it helps you create test boundaries. See what each mock you introduce does to your tested code using visual metaphors.

### Mocking Functions

Functions are at the heart of JavaScript logic. Learn how to mock functions for effective input-output testing. Create mock functions, spy on function calls, and mock function implementation to tap into the right behaviors of the tested code.

### Mocking Date and Time

Eliminate the side effects of ever-changing date and time in your tests. Learn how to freeze time and mock date/time-dependent code to ensure consistent test results across different runs and time zones.

### Mocking Globals

Explore how to mock implicit dependencies, in a non-intrusive way. Learn to mock global values, methods, and environment variables to create the perfect test setup without meddling with things you don't own.

### Mocking Network

Gain control over network communication and test your client-side code reliably. Intercept requests and mock responses using Mock Service Worker. Reproduce various network scenarios, from success and error responses to offline behavior and response timing.

### Mocking Modules

Understand when to use module mocking and explore alternative techniques before you do. Learn how to mock modules in a type-safe and efficient way using built-in APIs in Vitest.

## Who This Workshop Is For

This workshop is meant for all developers, both those who are new to automated testing and those who’ve been writing tests for years. If you are unsure when to introduce mocks into your test suite, or how to do that so you don’t have to refactor it the next day, this workshop was made specifically for you.

Mocking Techniques in Vitest

Epic Testing Bundle

Learn about the world of React component testing using Vitest and discover best practices that will help you write reliable and maintainable tests for your components.

Introduction to React Component Testing with Vitest Browser Mode

Workshop Introduction

Explore the history of browser-like environments, their advantages and disadvantages, and reasons to switch to actual browser testing.

Sunsetting JSDOM

Break JSDOM

Learn about the challenges of browser-like environments such as GSDOM, how it impacts component testing, and how to utilize Vitest browser mode as a solution.

Recap Of Sunsetting JSDOM

Vitest new browser mode promotes a proper component testing strategy, allowing you to run tests in actual browsers rather than simulated Node.js environments.

Vitest Browser Mode

Learn how to install Vitas Browser Mode dependencies and configure your React project for seamless browser-based testing of your components.

Streamline your testing process by updating your tasks to utilize Vitest's powerful browser mode capabilities.

Installation and Setup

Learn how to transform your existing test cases for React components by switching from React test library to Vitest.

Get started with Vitest Browser Mode and experience improved React component testing through well-structured concepts like locator objects and streamlined element selectors.

Migrate The Test

Learn how to make your browser testing more reliable and explicit by switching from the default preview provider to PlayWrite in Vitest.

Learn how to install and configure Playwright as a browser automation tool for Vitest, ensuring more reliable component testing for your web applications.

Playwright

Make sure your component tests include the necessary styles for both visual consistency and accessibility, by updating your testing setup.

Learn how to apply styles consistently to all component tests and use a global browser setup to handle unique situations.

Shared Assets

Learn how to configure Vitest to handle unit tests, integration tests, and component tests within the same codebase for efficient testing.

Understand how to distinguish between unit and browser tests with Vitest workspaces for better organization, smooth execution, and easier debugging.

Multiple Workspaces

Dive into the versatile world of Vitest Browser Remote, exploring installation, migration, custom asset loading, and best practices for component-level testing.

Outro Vitest Browser Mode

Improve your component testing knowledge through a guided exploration of accessibility selectors, user events, API mocking, element presence, and page navigation to ensure high-quality web applications.

Best Practices

Move beyond basic component tasks to interact with UI elements, just like real users do, for more effective browser automation testing.

Writing test cases to simulate user interactions for applying discount codes using Playwright and Vitest.

User Events

Network Mocking

Learn how to build reliable tests for element presence and disappearance in discount form applications, while avoiding false positives.

Explore techniques to test React components using Vitest, including waiting for elements to appear or disappear efficiently and accurately without inversing assertions.

Element Presence

Learn how to create a custom wrapper function in React Router to provide the missing routing context to your isolated component tests.

Discover how to use React Router's Memory Router to achieve better test boundaries and maintain component-level test isolation.

Page Navigation

Gain in-depth knowledge of web testing best practices and lay the groundwork for successfully debugging test failures.

Recap Of Best Practices

Learn to conquer failing tests with advanced debugging techniques in this exercise focused on component-level tests in the browser.

Debugging Tests

Learn helpful strategies for debugging component tests by examining the DOM state at different points during the test execution process.

Learn how to efficiently debug your DOM issues using the debug method from Vitest, locating specific elements and fixing layout problems.

DOM Snapshots

Uncover the power of the debugger statement in JavaScript and explore how to set up Visual Studio Code for debugging and attaching to browser tests.

Troubleshoot and debug failing tests more effectively with breakpoints and debug mode, making test execution stop so that you can examine the problematic steps.

Debugger

Learn debugging features such as in-line breakpoints and conditional breakpoints, and see how they can help you tackle the root cause of complex issues in your JavaScript codebase.

Learn how to use conditional breakpoints to effectively debug issues with React components and understand their implications in your tests.

Breakpoints

Find out how to quickly deal with failed tests while increasing productivity and embracing CI pipelines using a variety of JavaScript debugging techniques.

Recap Of Debugging

Improve your web development skills by learning advanced component testing methodologies, effective debugging techniques, and how to put your newfound knowledge into practice.

Get access to React Component Testing with Vitest

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