Efficiently test Error List component rendering with React Testing Library. Gain hands-on experience across diverse test cases.

Simulate DOM with JSDOM for React component testing, skip the browser. Utilize Testing Library, tackle challenges, and hone your skills.

Testing React Components with JSDOM

[00:00] So, let's pop open this file, and we need to add a JSDOM comment pragma at the top. So, by default, our tests are all running in Node, but for this particular test, even though we can server render React components and stuff, we're typically concerned about the client-side render of our components,

[00:20] and more often than not, you're going to want to test user events and stuff like that. So, we're going to add the VTestEnvironmentJSDOM thing here. So, VTestEnvironmentJSDOM. So, that turns this into a JSDOM test. Let's test that out, actually.

[00:38] So, we'll just say, test test. There we go. And we'll console.log window, and save that. And test is undefined. Of course, we're going to need to import, test, and expect from VTest. There we go. Okay. So, this is going to give us this global object.

[01:00] We've got a whole bunch of nonsense on this thing. We can also do document. Document. There we go. And there's our document. Okay. If we don't have this JSDOM pragma in here, then we save that, and it's not defined. So, that's what the pragma is doing, is it's giving us a simulated DOM environment for

[01:22] our lower-level tests that don't really make sense to run in a real browser, just because the extra weight that a real browser adds to our tests. And so, this is for when a simulated DOM environment using a tool like JSDOM can be quite helpful. But you do need to be aware that this is still running in Node.

[01:41] It's not a real DOM. And often people will blame testing library for things that are actually problems with the simulated DOM. Testing library runs in real browsers, as well as in a simulated DOM. And most of the time, problems that you have with testing library are probably a result

[01:59] of running with a simulated DOM, which is, yeah, it definitely comes with trade-offs. But this is still the way that I recommend you do these kinds of tests. And so, that's why we're doing it today. Okay, so let's actually write a real test.

[02:18] So, the form error list test, it shows nothing when given an empty list. We're going to do the easiest case first. We're going to need to import the error list component, there we go, from the forms.

[02:34] And we're also going to need to bring in a render and a screen, QRS. I like to try and alphabetize my imports, I don't know why. So, we bring in render. We're going to await that. So, this is async.

[02:51] In a recent version of React testing library, render has turned to an async operation. So, we're going to say await render error list. And with that then, that's going to populate our DOM. So, here's what we're going to do. We're going to use a screen.log or debug right here.

[03:11] And then we'll put a screen.debug right here. And so, here's the before and here's the after. Once we render that error list with no errors, then we do get this div. This is a div that's actually created for us by testing library when it renders our component.

[03:28] And so, because we're not rendering any errors, we're going to get null in return here. So, that's why this container, this div has no children. But we could also test out h1 and hello h1. And you'll see that that does appear inside the container.

[03:48] And so, this screen debug is actually a really, really helpful tool to give you an idea of what the DOM output looks like so that you can start querying around for things. So, what we want to do is if there are errors, then we say one, save that. And we've got a UL right here.

[04:05] So, what we're looking for is just to make sure that there are no list items. And in testing library, with the number of queries that you have, the one query that you use when you want to assert that something is not there is screen.queryBy and then we'll do the role variant. So, we're going to query all of the list items.

[04:26] And with that, we'll expect that to have length of zero. So, there should not be any of those. And that is failing, of course, because we changed our test there. So, let's get rid of that and save that. And let's see, we've got target cannot be null or undefined.

[04:47] Oh, that's interesting. We want to actually say query all by role. So, we want to get all of the list items. What queryBy role is going to do is it's going to find the one list item that's on the page and it's going to return null if it can't find it. We want to get an array of all of them. And so, that is how we go about doing that. We have a length of zero.

[05:08] Okay, awesome. And let's take a look at this to make sure we can break it. So, if I say li hi, then we do in fact break it. So, we are executing the code that we think we are. And of course, you can run the code coverage on this test to make sure that you're covering

[05:26] the lines of code that you think you are. But again, whenever you do that, you want to focus on the experience of what the use case is rather than the lines of code. All right. So, just a quick review. We have VTestEnvironment.js DOM to give us a DOM to work with.

[05:44] We grabbed render and screen from testing library. And then we await render error list and expect query all by role list item to have a length of zero. So, that's our first test with testing library.

Error List Component with React Testing Library

[00:00] In this exercise, we're going to be testing the error list component, so it's rendering JSX. We need to be able to render that JSX in the same way that it's going to be rendered in our application, that is, to the DOM. Now, we're going to be using a library called Testing Library or React Testing Library for this.

[00:17] I wrote this a few years ago to make testing React a lot easier, and it is, and it's great. So, you're going to be able to use React Testing Library to test this component. We've got a couple of cases here, so get to it.

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## End-to-End Testing with Playwright

With end-to-end (E2E) testing, you can validate a web app from the user's perspective. This is the closest you can get to a real user interacting with your app. In this section, you'll learn the ins and outs of writing a test with Playwright:

- Best practices for setup before running tests
- Simulating user actions like interacting with the UI to perform a search
- Creating a new user in the database
- Cleaning up after tests have run
- Using playwright fixtures for reliable setup/teardown

## Mocking & Authentication for E2E Tests

When your application relies on external services, you need to have a way to test them without actually using them. Similarly, you don't want to fully onboard a new account every time you test an authenticated user flow. In this section, you'll learn how to re-use the same mocks we’ve been using for development to mock third-party services and simulate logging in:

- Use Mock Service Worker to intercept network requests
- Replace email verification with a local file solution
- Attach cookies to Playwright
- Reusing 2FA logic for local testing
- Testing behavior with different HTTP responses

## Unit Testing

Sometimes you’ve got some really complicated business logic in your app. Business logic that is critical to your application. For this stuff, it’s nice to package it up in its own function or module to keep all that logic in one place. This is the perfect situation where lower level unit testing comes in handy. Here, we'll dive into unit testing with the Vitest framework to ensure that each function and module behaves as expected:

- Organizational best practices
- Asserting outcomes with `expect`
- Recording function calls with spies
- Specifying test behavior with Vitest hooks
- Keeping test output clean to avoid cluttering up the terminal

## Component and Hook Testing

When building React components, you should focus on two users: the user who interacts with a component, and the developer who renders it. By using Testing Library, we can avoid mocking React and its hooks and instead test components as they would be used in a real app:

- Render components with Testing Library
- Simulate the DOM environment on a per-test basis
- Querying for missing elements
- Testing hooks in isolation from React
- Stubbing React context
- Cleanup after testing

## Authenticated Integration

Similar to higher-level E2E tests, it is often necessary to simulate an authenticated user. However, we don't want to test the entire user flow every time we make a change. In this section, you'll learn how to test authenticated operations without the overhead of a full E2E test:

- Generating random session IDs
- Associating sessions with users
- Testing authenticated routes
- Asserting user state in responses

## Custom Assertions

Writing tests is good; writing readable and maintainable tests is better. Custom assertions can make your test code easier to understand and modify. Here you'll learn to encapsulate complex checks into simple, understandable assertions:

- Create matchers for specific states
- Share assertions across tests
- Add custom assertions to TypeScript definitions
- Format test output with colors for readability

## Test Database

There are some decisions to make when writing tests that interact with the database. Testing with the development database has benefits, but requires us to remember to delete data after each test. By using a test database, we can avoid accidents while still being able to run our test suites:

- Set up a test-specific database instance
- Seeding a minimal amount of data
- Defining a global setup for Vitest
- Understanding the importance of module import order

Learn how to write tests that cover all of your backend and frontend code. Web Application Testing covers unit testing, E2E, integration testing, and more!

Web Application Testing

Kent C. Dodds

Full Stack Vol 1

Intro to Web Application Testing Workshop

Intro to Web Application Testing 

Intro to End-to-End

Automate tests seamlessly in Playwright UI mode, mirroring manual tester actions. Validate search feature with Playwright's robust tools and intuitive interface

Playwright tests for user interactions, page navigation, search box inputs, and assert URLs, list elements, and items to test web app search functionality.

Writing and Asserting Playwright Tests for Search Functionality

Writing Automated Tests with Playwright UI Mode

Master isolated tests in Playwright and Node for better control, independence, and reliability. Import and run essential APIs for self-sufficient testing.

Create, manipulate URL with search parameters, display user data using encoding. Elevate your app's user data handling skills.

Creating and Interacting with User Data

Isolating Tests for Better Reliability and Flexibility

Clean up test data to maintain test isolation in end-to-end testing. Prevent data buildup in the development database, ensuring smooth, reliable workflows.

Incorporate user deletion in setup and teardown for a pristine testing environment, eliminating unwanted data and ensuring a clean slate for every test.

Proper Setup and Teardown of Testing for Database Cleanup

Test Isolation in End-to-End Testing

Utilize Playwright fixtures to guarantee thorough database cleanup, eradicating test-created user data, bypassing potential pitfalls from alternative methods.

Use Playwright fixtures for custom test objects, properties, behaviors, execute functions strategically, and manage data cleanup efficiently.

Playwright Fixtures for Testing

Implementing Fixtures to Ensure User Deletion in Playwright Tests

Take a break, nourish yourself, hydrate, and jot down your learnings to keep your brain sharp. Let's continue the great work with more testing ahead!

Dad Joke Break E2E

End-to-End

Address HTTP/S validity with a mock server and stub, this makes it easy to ensure that a client's response is consistent

Intro to E2E Mocking

Capture, save verification codes for smooth server-test automation communication.

Master Node.js email read/write with the File System module. Save, retrieve email data for testing efficiently.

Handling Emails in Node.js using File System

Writing Emails to the File System for Test Automation

Quickly grasp requiring and using disk-stored email data in tests for successful content reading. Crucial for test setup and execution.

Enhance process-to-process communication in Node.js using the secure file system method. Elevate data transfer and parsing capabilities.

Communicating Between Processes with File System in Node.js

Reading Email from Disk in Test Environment

Quickthink about the punning methods you will employ to share skeins of mirth with your fellow yo-cards

Dad Joke Break E2E Mocking

End-to-End Mocking

Learn how to simulate an authenticated user in your tests by generating and adding cookies to the browser context, improving test efficiency and isolation.

Intro to Auth E2E

Master end-to-end user flow tests, streamline authentication, and navigate login, profile editing, 2FA, and login verification.

Simulate user login, set cookies in browser tests to mimic web app authentication accurately.

Login and Setting Cookies for Browser Testing

End-to-End User Flow Testing and Authentication Utility

Dad Joke Break Auth E2E

Authenticated End-to-End

Intro to Unit Test

Craft solid unit tests for getErrorMessage, covering various scenarios and input-based error messages. Test pure and impure aspects thoroughly.

Master unit testing for utility functions, cover error handling, and achieve full code coverage with tools like coverage reports.

Writing Unit Tests for Utility Functions

Unit Testing a Function for Error Messages

Minimize test output logs, mock console.error for cleaner testing. Master spies for focused, effective testing without excessive console noise.

Utilize spies to track, assert console.error calls in tests. Ensure correct arguments and preserve valuable error info.

Testing Console Error with Spies

Managing Test Output and Error Logging with Console Mocking

Utilize Playwright testing hooks for error restoration and default mock restoration to enhance test stability.

Learn how to restore mocks by default, capture and handle console errors, and create a shared console error setup for efficient JavaScript testing.

Effective Error Handling and Console Capture Testing

Implementing Test Hooks for Error Restoration in Playwright

Create a setup file for automatic inclusion of essential files in all test files, closely simulating the production environment for effective testing.

Set up a test directory with setup files using VTest to automate configuration and common tasks. Ensure smooth test execution and robust error handling.

Setting Up Test Environment and Utilizing Setup Files with VTest

Creating a Setup File for Test Environment Setup

Dad Joke Break Unit Test

Unit Testing

Intro to Component Testing

Fix test failures from DOM manipulation with proper cleanup techniques for reliable, efficient testing.

Maintain test isolation, eliminate dependencies on test state, and ensure clean execution in Testing Library with effective test cleanup.

Ensuring Isolation and Proper Test Execution

Proper DOM Cleanup for Reliable Testing

Dad Joke Break Component Test

Component Testing

Intro to Hooks

Create a double confirmation feature in React with a custom hook. Explore implementation,testing with RenderHook and Act. Prevent accidental actions effectively

Master custom React hook testing with RenderHook and Act from Testing Library React. Access hook properties through result.current for precise testing.

Testing Custom React Hooks with RenderHook and Act

Double Confirmation Feature

Test hooks with flexibility. Use custom test components or the render hook utility. Tailor your approach to your testing needs and preferences.

Create test components for thorough React hook testing, ensuring API contracts, and validating state changes accurately with Testing Library React and UserEvent

Testing React Hooks

Custom Test Components vs Render Hook Utility

Dad Joke Break Hooks

Hooks

Ensure test-driven development (TDD) by writing testcases from the get-go and developing integration tests quickly in isolation.

Intro to Testing Remix 

Master Remix stubs for isolated component testing, handle edge cases, simulate user states without full end-to-end testing.

Use CreateRemixStub for Remix components with mock data. Test integration with React Testing Library for proper rendering and DOM element waiting.

Rendering Components with Mock Data

Creating a Stub for Testing Component Logic in Remix

Fix a failing test by adding a parent route granting access to root data. Ensure proper rendering and testing of the username route in authenticated settings.

Create authenticated integration tests in Remix by configuring root routes, loaders, and context for precise testing of user interactions.

Creating Routes and Context in Remix

Creating a Parent Route for Accessing Root Data

We interrupt your couch time for this important reminder. Oh, and to keep you feeling healthy and vibrant.

Dad Joke Break Testing Remix 

Testing Remix

Learn how to mock APIs using MSW to enhance testing reliability, handle different scenarios, avoid dependencies, and ensure test isolation.

Intro to Http Mocking

Manually test and modify GitHub sign-in callback in your app. Adjust user association, validate response cookies, and location headers for robust functionality.

Simulate OAuth2 flow, effectively mock GitHub API requests in tests. Ensure robust verification of authentication and API integration in your app.

Testing OAuth2 Flow and Mocking GitHub API Responses

GitHub Sign-In Callback

Override HTTP interceptors for GitHub API token requests in testing, handle errors efficiently, export and access the server, and implement cleanup.

Master error case testing in a mock API environment. Verify failure handling, page redirection, and console error capture. Maintain test isolation with cleanup.

Testing Error Handling and Assertions with Mock API Calls

Testing Error Handling in GitHub API Interceptor

Learn how to avoid repeating test code by creating reusable functions and avoiding excessive duplication, ensuring efficient and maintainable testing workflows.

Organize code better with bottom setup functions, reduce repetition, and boost readability through parameterization and code sharing.

Efficient Code Organization with Setup Functions

Streamlining Repetitive Test Setup for Optimal Efficiency

Dad Joke Break Http Mocking

HTTP Mocking

Intro to Auth Integration

Master testing authenticated requests & connections post-login. Simulate sessions, verify for code reliability.

Master user setup, authenticate, and manage connections, including GitHub and DB users, sessions, and test cleanup. Deep dive into authentication.

Creating and Authenticating Users for Connection Setup

Testing Authenticated Requests and Connection Creation

Verify GitHub login session creation with assertions. Cover scenarios like connecting accounts and non-logged-in users.

Extract, check, parse server response's session cookie for user authentication, ensuring DB session creation.

Verifying Session Creation and User Authentication

Assertions for GitHub Login Session Creation

Swap fake data with real user info in routes, use utilities for seamless database user insertion and deletion.

Real DB interactions for user creation/deletion, image addition, request authentication in integration tests. Full UI coverage, no heavy mocking.

Authentication in Database Integration Tests

Integrating Real Database with User Routes

Dad Joke Break Auth Integration

Authenticated Integration

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Intro to Custom Assertions

Enhance test assertion readability and functionality by creating custom matchers like assertRedirect. Elevate code clarity and error messages.

Elevate your testing game with custom assertions in Jest. Create "to have redirect" and more for precision. Organize in a test util directory for collaboration.

Custom Assertions with Jest's Expect Library

Custom Matchers for Assertions

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Dad Joke Break Custom Assertions

Custom Assertions

Extend the Gradle plugin to suit the needs of your projects. Learn about exploring a Cucumber-JVM Gradle boolean condition or approach using

Intro to Test Database

Set a test database with a URL before importing Prisma for seamless client testing. Master import order and setup for success.

Learn how to properly set up an isolated database for testing purposes using Prisma and dynamic imports, ensuring a clean and efficient testing environment.

Setting Up an Isolated Database for Tests

Setting Up a Test Database for Prisma Integration Tests

Learn how to solve conflicts when running tests simultaneously by setting up individual test databases to avoid shared state and data interference.

Learn how to create and manage isolated test databases using unique identifiers, allowing for efficient and independent testing processes.

Isolating Test Databases for Efficient Testing

Managing Test Databases for Parallel Testing

Speed up test execution with a global setup module. Enhance efficiency for faster, full database tests.

Learn how to set up a base database for faster test execution, avoiding repetitive migrations, and utilizing the real database environment efficiently.

Optimizing Test Setup with Global Database Configuration

Optimizing Test Setup

Take a well-deserved break before applying the acquired knowledge to your own projects. Well done!

Dad Joke Break Test Database

Test Database

Discover how to set up and integrate various testing tools, both at the UI and lower levels, to enhance your app's stability and facilitate easier test creation

Web Application Testing

Web Application Testing

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Error List Component with React Testing Library

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