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

[00:00] So I'm going to create this file right next to it. I like to co-locate my lower level tests like this. So we're going to say miss.test.tsx, or ts. There we go. But we have a lot of utilities in here. And so I'm going to differentiate this one just a little bit by adding another dot in here.

[00:19] And we'll say error message. And actually, this is totally legit. I will pretty often have multiple files that test different aspects of a utilities file like this. Especially if they require a different setup and stuff like that, that could be really useful.

[00:36] OK, so with this now, we can import test and expect from vTest. All right. And then we'll add our test, the error object returns message.

[00:51] So if we just do a regular error of some kind, then we're going to expect that getError message for that error should be the same thing. So let's run vTest npm test. And that will run vTest on our tests.

[01:11] And there we go. That test totally works. And this is a very important thing. You need to do this. Make sure your test can't fail, because it's very possible that you're not testing the thing you think you are. And it's even better than breaking the test itself. Go into the source code and see if you can break that. Return high.

[01:30] And if you can break it from the source code, then you're like, yes, I am running that line of code for sure. So that helps a lot. Definitely recommend it. OK, now there's one other thing I want to change about this. And that is, what if somebody was silly

[01:44] and said, if the error.message is this? That would be a silly thing to do. And then we have return high. OK, this is just an example.

[02:02] Our function is totally busted in a terrible way. But there's not really anything communicating to the reader of the test that this is an error, is not some sort of special string that is treated specially. And so for that reason, I actually

[02:19] generate as much of my test data as possible. So we're going to say faker, to use faker to generate, maybe not a sentence, maybe just a couple words. We'll generate two words there. And then we'll make sure that the error message is the same.

[02:35] So here, the way I want to do this is we'll say, this is our message. And then we expect this to be the message. And there we go. We successfully failed. And so we can now fix this. And there we go.

[02:54] Now our test should be passing. And we won't have that problem anymore. And we communicate to readers of the test that, yes, that is actually any message. Whatever the message is, that's what this function is doing for us. OK, so let's handle this case now.

[03:11] If the string or the type of error is a string. And so we'll say test. And actually, you know what, before we do that, let's take a quick opportunity to run npxv test, no watch.

[03:27] We need, good grief, no watch and coverage. So this will run all of our tests, of which we only have one. And it will include a coverage report. So we can actually open the coverage and index HTML right there.

[03:45] That'll open up in our browser. There's our dad joke. So here is what the coverage report looks like. We'll look in these details. And here's miss. And we only have one test, so there's not a lot of coverage. But you'll notice in this coverage report, it's going to show us, hey, that's not being covered right now, it's highlighted.

[04:05] So we are covering this statement right here, this if statement, but we're not falling into the consequent. And so that's why that's being highlighted. So we're only covering half of the branch. We are covering this, because we end up in here, but we actually don't get past this. So when I see a coverage report like this,

[04:23] I'm constantly just thinking, OK, so that's great. What are the use cases that I'm missing? So you want to look at the code and then think about the use cases, because that's what's actually important is the use cases, not the particular lines of code,

[04:40] necessarily, because you can sometimes overfit to those use cases. So this coverage report can be pretty helpful if you're trying to figure out, OK, what other tests do I need to write? And other tests we need to write include that the error is a type of string, and if it is, then it'll return that. And then the other, it would be a situation

[04:59] where we're passing just something totally random. User doesn't know what it is. So let's cover those pieces of code as well. Coming over here, we're going to say, let's run our test again in watch mode. Sweet.

[05:17] So the string returns itself, and that's going to be our function here. Then, yeah, there we go. That works perfect. Thanks, Copilot. The string returns itself. And of course, you want to check that, and yep, that works. So we're good.

[05:35] And then let's have a test. Oh, and you know what? I just realized that we're generating a two-letter word. We want words. We want two words. There we go. That should be better. OK, so this last one is going to be undefined falls back to unknown. And so then we can just say, Copilot's

[05:55] going to get this one for me. I know it, Copilot. Yes, thank you. So if we pass in undefined or pass in some random object or whatever, undefined works fine, then the result should be unknown error, actually, I think is what we return. Yep, unknown error.

[06:14] And that gets our test passing. If I change this, then that's going to fail, so that's good. And what's interesting is we've got this standard error output. Ooh, that's not good. I don't like seeing that. We'll talk about that more later. But let's run that coverage report again to make sure that we're covering everything

[06:33] that we were hoping. And I can just open that up again. And boom, we're covering the whole function. We can look at this line, or this if statement is executed three times, apparently. So that's interesting. So there you go. That is our first unit test.

[06:51] We've got some more work to do, but hopefully that was a good time for you.

Unit Testing a Function for Error Messages

[00:00] Here's the function that we want to test, getErrorMessage. It takes an unknown argument. If that's a string, it returns an error. If it's an object and it has a message and the message is a string, then it returns that message. Otherwise, it's going to log to the console. That's going to be a bit of a challenge for us later. And it will return unknown error.

[00:18] So your task is to write a test for this. It's a perfect use case for a unit test because it's got a little bit of logic in there. And it is a pure function. Well, it's sort of pure, actually. It's a little impure right here. But for the most part, it's mostly pure. So the basic tests are going to be a little easy.

[00:36] It takes an argument, returns a value, that sort of thing. So you're going to have a good time with this one. 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

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

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

sanityVideoMuxId: gndUuMl8O02HCDPqYUGRa1o2oUxoiYsRoakUQ802ZtPnc

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

sanityVideoMuxId: pmPD6AekZgJhQP2kES5V2aErPtkkyA00GTSVfLcRp4ys

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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Unit Testing a Function for Error Messages

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