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

[00:00] So, we've got a failing test. Let's take a look at what that failing test looks like. So, it shows nothing when given an empty list. That works. Shows a single error, and then once we say shows multiple errors, then that's a problem. Now, you might think at first glance that, okay, so this test is the one that has the problem. But check this out.

[00:16] If I say, alright, I want to do this one only, dot only, that, and now it's suddenly passing. That is a great sign that you are not cleaning up after yourself in another test. If it fails when it's run with other tests, but then succeeds when it is run by itself,

[00:32] then you're not cleaning up after yourself. Another situation that can happen is if it succeeds when it runs with all the tests, but fails when it runs by itself. That means that your test relies on state that's set up in another test. Again, you're not cleaning up after yourself properly. And so that's what's going on here.

[00:48] If we add a screen.debug to the first line of this shows multiple errors, we're going to see that we've got a div right here. So that's the spec. That's the div that's created from this first render. And then we've got another div right here. This is the container for

[01:04] this second render call. And so by the time we get to this render call, we're going to have three divs. If I move this down there, then we can take a look at that. We've got the second one, and then here's the third one. And so when we're looking for all of the list items, we're going to

[01:20] get this one in addition to these two. And that is what's causing our error. So we just need to make sure we clean up after ourselves. And there's an easy way to do that. With Testing Library React we say clean up. And then you can call clean up at the end

[01:36] of each one of these. And we'll await clean up. And await clean up on both of those. And now this test will pass. And of course you'll want to do that on all of these. But we need to do

[01:52] I don't want to have to do that at the end of every one of my tests. And of course if the test fails then the clean up will fail as well. So we're going to add an after each after each from vTest and we'll call clean up there. You could also do it this way if

[02:08] you so desire. And what that is going to do is automatically clean up after every one of our tests so that we're totally clean by the time we get to every single one of our tests. Which is exactly what we want. So with that now when we

[02:24] do a screen debug the body is totally empty. Now another thing that I want to show you really quick as a part of this is just that we have another utility. Just like our screen.debug we have another utility that we can use that can be kind of helpful. It's called

[02:40] screen.logTestingPlaygroundURL. And with that it logs this URL that you can copy and open it up in a browser and it will take the DOM and stick it in this

[02:56] input right here. And then it will render that right over here and then you can click on those things and it will give you a suggested query for you. Autocomplete that in there and even tell you if there's a better one to be had. And so

[03:12] it's a pretty cool tool that will make it a little bit easier since we don't have a real browser environment as we're testing in JSDOM. So that is logTestingPlaygroundURL. Another thing that I'll mention is that some of you might be a little confused if you've used Testing Library before

[03:28] because you've never had to do this cleanup before. And that's because Testing Library React will actually look for a global after each or a global teardown and if that does exist then it's going to register this cleanup for you automatically. We have VTest configured to not

[03:44] set all of these values as global because I actually like that I could execute this file as is and not have to do any global setup for these global variables. That's an intention on my part to not make

[04:00] these things global and because we don't do that we have to set up this cleanup ourselves. Which definitely is a bit of a drawback but I think that it's worth the effort especially since it's not a whole lot of effort because we can literally just take

[04:16] this and move it over to our setup test environment and we just stick that right here and bring in cleanup and bring in after each and now I can just delete this here and delete that there and the whole thing still works.

[04:32] And so it's not a whole lot of extra work to deal with the fact that we're not doing things in a global context and to me that's totally fine. So there you go. That is doing cleanup for a testing library to make sure that your tests are all isolated from each other.

Proper DOM Cleanup for Reliable Testing

[00:00] So, Kelly finished the test for us, and feel free to delete these tests and write them yourself if you want to practice, but they're not working. There's a problem with them, and it has to do with the fact that we're mucking with the DOM and not cleaning up after ourselves. So, your task is to handle the cleanup. This will be pretty quick. We'll see you when you're done.

We all know the drill. The code works on your machine but you didn’t realize the impact of the change you made and it breaks in production. This problem grows exponentially as your application’s size and usefulness grows. Unpredictability can be a developer's worst nightmare.

However, many developers find it difficult to effectively test their code. Manual testing gets tedious fast. Complex logic and async code can be tricky to test effectively.

The Full Stack Testing Workshop will equip you with the tools you need to ensure your app works now and in the future. You'll learn how to write modular, maintainable tests that cover all of your code, from the backend to the frontend.

As the author of the de-facto standard testing library for web development (called eh… Testing Library), I have some solid opinions that have led many teams to much more confidence shipping their code. Let’s get you some of that confidence.

## 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

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

Error List Component with React Testing Library

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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Proper DOM Cleanup for Reliable Testing

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