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

[00:00] We write tests to make sure that our code, in this case, our components, fulfill their purpose. And the purpose of the discount code form is to be able to apply a given discount to imaginary checkout process. So let's implement this little user journey in the test itself. First, I will rename the test because it will no longer just render the form.

[00:19] It will actually make sure that the user is able to apply the discount code. Next, let's enter the code into the appropriate input. So we already have this input here and we got it by label text in the previous exercise. So now I want to interact with this element. But the first thing I will do, I will actually remove this to be visible assertion.

[00:38] And instead, I will call this input and then fill and provide the value I want to fill into that input, our discount code. For example, Epic 2025. So why did we get rid of the visibility assertion? Well, because interacting with the element implies its visibility and accessibility. So we don't have to repeat that assertion.

[00:57] We just can interact with the element and gain the same result. So here, we're entering the discount code into the input. And this fill method on the locator returns us a promise that will be resolved once the browser is done typing this value in. So now that we enter this code, we have to apply it by clicking on the discount button.

[01:17] And it's the same logic here. We don't need this visibility assertion anymore. Instead, we can just grab our button and call the click method on it. That's going to force Playwright to click on this button and the visibility of the button is once again implied. So now we have a tiny user journey here, entering the value and clicking on the button to submit the form.

[01:36] And it's finally the time for us to reflect some expectations. So what is supposed to happen as the result of these actions? If I take a look at this discount code form, I can see that once the discount is applied, it gets rendered for the user in this paragraph that says discount,

[01:52] then the discount code, and the discount percentage in the parentheses. That's exactly what I want to reflect in my test to make sure that the component actually displays what the user expects to see. So I will add this final assertion. I will write expect element.

[02:09] I will locate this element by its text because you know that paragraphs don't have any roles and any accessible names. So get by text and provide this text as is. So this discount is visible for the user.

[02:24] And you can see that I'm including the actual value I entered in this assertion just to make sure that we're displaying the correct code. And finally, I need to add the assertion itself. So here I will chain to be visible.

[02:40] Now that we have this interaction described, let's run this test. So npm test. And we can see it passing. So let's recap what we did here. We still locating the elements the same way we did before using accessible locators.

[02:55] We dropped the explicit visibility assertion because now it's implied using this interaction methods like fill or click. If you explore your locators, you can see that Vitest actually gives you a bunch of different methods to call on them. But you may be more familiar to something like user event from React testing library, right?

[03:14] That object still exists with browser mode. If you go to this Vitest slash browser slash context, you can access user event object as well and use it like you normally would, for example, for filling some values and simply the call signature changes. So why have two different approaches here?

[03:33] Well, this user event object actually taps into locators for the implementation. So whenever you can, you can utilize locator methods directly. But the user event object provides a few additional higher level interactions. For example, you can have user event upload or cut or paste.

[03:52] So as a rule of thumb, rely on the built-in methods on your locators. And if you want a little bit more, then reach for the user event from Vitest. And of course, once we're done interacting with the form, we write the assertion to make sure that the correct element, the correct discount confirmation is displayed for the user.

[00:00] The component task you have right now already gives you some value, but it can give you more. All it does right now is locates the elements on the page and make sure that they are visible. And that makes sense because when users open your app, they want to see those elements on the page, but they don't want just to stare at them. They want to interact with them. They want to use that UI to help them solve their tasks.

[00:19] Historically, when we were rendering our components and running tasks in browser-like environments, we had to simulate user events, events like change or click. But since now you're able to tap into the power of actual browser automation, you don't have to do that. You can actually reproduce real user events in the browser because the users hover with

[00:37] their mouse and click on your elements and type with their keyboards. And that's exactly what you should do in your tests as well. In this exercise, your task will be to expand on the existing test and actually interact with those elements, to fill in the discount code and click on the button to submit it. So follow the instructions in the task suite and have the task passing.

[00:57] And as always, once you're done, come back so we can discuss the solution together.

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

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

Queries

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.

React Component Testing with Vitest

React Component Testing with Vitest

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User Events

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