Utilizing Jest Mock Functions for Effective Testing
Emphasizing User Interaction and Behavioral Testing
Handling Asynchronous Data Loading in Tests
Benefits of Testing the Contract in Component Development
React Native Testing Library offers a robust approach to testing React Native applications, emphasizing accessibility and usability. Components tested using this library are inherently more accessible to users with different abilities. For instance, screen readers, widely used by visually impaired individuals, can effectively interact with components when they are structured with accessibility in mind. To achieve this, developers should add accessibility labels to non-text elements, such as images and SVGs, ensuring that screen readers can describe these elements audibly.
When writing tests, the React Native Testing Library suggests using queries that reflect how users interact with the application. Queries like 'getByText', 'getByLabelText', and 'getByPlaceholder' are prioritized because they simulate user interactions with the app, making tests more realistic and user-centric. This approach ensures that tests are not only validating the code but also confirming the user experience, making applications more inclusive and robust.
One of the key aspects of testing is the ability to mock functions and modules. Jest provides a powerful feature called mock functions, which allow developers to simulate the behavior of real functions in a controlled way. This is particularly useful when testing components that rely on external data or interactions. By using 'jest.fn()', developers can create mock functions to verify that certain functions are called and that they receive the expected arguments. This technique helps isolate the component being tested from external dependencies, ensuring that tests are focused and reliable.
Another critical aspect of testing with React Native Testing Library is handling user interactions. User inputs, such as clicks and text inputs, are considered inputs to the component, similar to props. The library provides the 'fireEvent' API to simulate these interactions within tests. While 'fireEvent' is the primary method used in React Native, the React Testing Library for web applications recommends 'User Event' for more realistic simulations. Unfortunately, 'User Event' is not available for React Native, but 'fireEvent' serves a similar purpose, allowing developers to test how components respond to user actions.
Testing asynchronous data loading, such as API requests, requires careful handling to ensure that tests remain deterministic and reliable. One approach is to mock the API calls using Jest's module mocking capabilities. By intercepting the module responsible for making HTTP requests, developers can simulate responses without relying on actual network calls. This not only speeds up tests but also makes them more reliable by eliminating the variability of network conditions. Developers can use 'jest.mock()' to replace real modules with mock implementations, providing controlled data for tests.
To effectively test asynchronous operations, developers can use the 'findBy' queries provided by React Native Testing Library. These queries wait for elements to appear on the screen, allowing tests to handle asynchronous data updates gracefully. For instance, when testing a component that fetches data on render, developers can use 'findByText' to wait until the expected data appears in the UI, ensuring that the test does not proceed until the component has fully rendered the desired state.
Testing the contract of a component involves focusing on the inputs and outputs rather than the internal implementation details. This approach leads to more maintainable and robust tests. By testing the contract, developers ensure that components behave as expected when given certain inputs, producing the anticipated outputs. Props and user interactions serve as inputs, while rendered UI and function calls are considered outputs. This methodology allows developers to refactor components internally without affecting the tests, as long as the contract remains unchanged.
In conclusion, mastering React Native Testing Library involves understanding the importance of accessibility, utilizing Jest mock functions, and effectively handling user interactions and asynchronous operations. By focusing on testing the contract of a component, developers can ensure that their applications are robust, reliable, and accessible to all users. This approach not only improves the quality of the code but also enhances the overall user experience, making applications more inclusive and user-friendly.
Watch full talk with demos and examples:
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Are you satisfied with your test suites? If you said no, you’re not alone—most developers aren’t. And testing in React Native is harder than on most platforms. How can you write JavaScript tests when the JS and native code are so intertwined? And what in the world are you supposed to do about that persistent act() warning? Faced with these challenges, some teams are never able to make any progress testing their React Native app, and others end up with tests that don’t seem to help and only take extra time to maintain.
But it doesn’t have to be this way. React Native Testing Library (RNTL) is a great library for component testing, and with the right mental model you can use it to implement tests that are low-cost and high-value. In this three-hour workshop you’ll learn the tools, techniques, and principles you need to implement tests that will help you ship your React Native app with confidence. You’ll walk away with a clear vision for the goal of your component tests and with techniques that will help you address any obstacle that gets in the way of that goal.
you will know:
- The different kinds React Native tests, and where component tests fit in
- A mental model for thinking about the inputs and outputs of the components you test
- Options for selecting text, image, and native code elements to verify and interact with them
- The value of mocks and why they shouldn’t be avoided
- The challenges with asynchrony in RNTL tests and how to handle them
- Options for handling native functions and components in your JavaScript tests
Prerequisites:
- Familiarity with building applications with React Native
- Basic experience writing automated tests with Jest or another unit testing framework
- You do not need any experience with React Native Testing Library
This workshop has been presented at React Advanced 2022, check out the latest edition of this React Conference.
FAQ
React Native Testing Library is a framework that allows you to test React Native components in a way that simulates user interaction as closely as possible, ensuring your tests focus on component behavior rather than implementation details.
You can access the React Native Testing Library repository by visiting the URL provided in the workshop, which is linked to the Git repository containing exercises and resources for learning and practicing component testing in React Native.
Using Jest with React Native Testing Library provides a powerful assertion framework that helps in writing tests that are more descriptive and easier to maintain. Jest also supports mocking and spying, which are essential for testing components in isolation.
React Native Testing Library is primarily focused on testing individual components and their integration. For end-to-end testing in React Native apps, tools like Detox or Appium are more suitable.
To handle asynchronous events, React Native Testing Library provides utilities like 'waitFor' and 'findBy' queries that allow you to wait for certain elements to appear or change state before proceeding with your assertions.
Testing the contract refers to focusing on the expected inputs and outputs of a component, ensuring that it behaves correctly with given inputs and produces expected outputs. This helps in building reliable and maintainable components.
You can mock modules using Jest by using 'jest.mock()' to replace the actual implementation with a mock function or object. This allows you to simulate module behavior and control the inputs and outputs for your tests.
This workshop on React Native Testing Library covers various topics including testing components, user interaction events, mocking, and testing API calls. The speaker emphasizes the importance of testing the contract of a component and provides practical examples and exercises. Just module mocking is recommended as a portable solution for mocking modules. The workshop encourages exploring different testing strategies and provides additional resources for further learning.
React Testing Library is a great framework for React component tests because there are a lot of questions it answers for you, so you don’t need to worry about those questions. But that doesn’t mean testing is easy. There are still a lot of questions you have to figure out for yourself: How many component tests should you write vs end-to-end tests or lower-level unit tests? How can you test a certain line of code that is tricky to test? And what in the world are you supposed to do about that persistent act() warning? In this three-hour workshop we’ll introduce React Testing Library along with a mental model for how to think about designing your component tests. This mental model will help you see how to test each bit of logic, whether or not to mock dependencies, and will help improve the design of your components. You’ll walk away with the tools, techniques, and principles you need to implement low-cost, high-value component tests. Table of contents- The different kinds of React application tests, and where component tests fit in- A mental model for thinking about the inputs and outputs of the components you test- Options for selecting DOM elements to verify and interact with them- The value of mocks and why they shouldn’t be avoided- The challenges with asynchrony in RTL tests and how to handle them Prerequisites- Familiarity with building applications with React- Basic experience writing automated tests with Jest or another unit testing framework- You do not need any experience with React Testing Library- Machine setup: Node LTS, Yarn
The web has evolved. Finally, testing has also. Cypress is a modern testing tool that answers the testing needs of modern web applications. It has been gaining a lot of traction in the last couple of years, gaining worldwide popularity. If you have been waiting to learn Cypress, wait no more! Filip Hric will guide you through the first steps on how to start using Cypress and set up a project on your own. The good news is, learning Cypress is incredibly easy. You'll write your first test in no time, and then you'll discover how to write a full end-to-end test for a modern web application. You'll learn the core concepts like retry-ability. Discover how to work and interact with your application and learn how to combine API and UI tests. Throughout this whole workshop, we will write code and do practical exercises. You will leave with a hands-on experience that you can translate to your own project.
Introducing FlashList: Let's build a performant React Native list all together
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In this workshop you’ll learn why we created FlashList at Shopify and how you can use it in your code today. We will show you how to take a list that is not performant in FlatList and make it performant using FlashList with minimum effort. We will use tools like Flipper, our own benchmarking code, and teach you how the FlashList API can cover more complex use cases and still keep a top-notch performance.You will know:- Quick presentation about what FlashList, why we built, etc.- Migrating from FlatList to FlashList- Teaching how to write a performant list- Utilizing the tools provided by FlashList library (mainly the useBenchmark hook)- Using the Flipper plugins (flame graph, our lists profiler, UI & JS FPS profiler, etc.)- Optimizing performance of FlashList by using more advanced props like `getType`- 5-6 sample tasks where we’ll uncover and fix issues together- Q&A with Shopify team
Compared to unit testing, end-to-end testing aims to interact with your application just like a real user. And as we all know it can be pretty challenging. Especially when we talk about Mobile applications. Tests rely on many conditions and are considered to be slow and flaky. On the other hand - end-to-end tests can give the greatest confidence that your app is working. And if done right - can become an amazing tool for boosting developer velocity. Detox is a gray-box end-to-end testing framework for mobile apps. Developed by Wix to solve the problem of slowness and flakiness and used by React Native itself as its E2E testing tool. Join me on this workshop to learn how to make your mobile end-to-end tests with Detox rock. Prerequisites- iOS/Android: MacOS Catalina or newer- Android only: Linux- Install before the workshop
In the ever-evolving landscape of software development, ensuring the reliability and functionality of APIs has become paramount. "API Testing with Postman" is a comprehensive workshop designed to equip participants with the knowledge and skills needed to excel in API testing using Postman, a powerful tool widely adopted by professionals in the field. This workshop delves into the fundamentals of API testing, progresses to advanced testing techniques, and explores automation, performance testing, and multi-protocol support, providing attendees with a holistic understanding of API testing with Postman. 1. Welcome to Postman- Explaining the Postman User Interface (UI)2. Workspace and Collections Collaboration- Understanding Workspaces and their role in collaboration- Exploring the concept of Collections for organizing and executing API requests3. Introduction to API Testing- Covering the basics of API testing and its significance4. Variable Management- Managing environment, global, and collection variables- Utilizing scripting snippets for dynamic data5. Building Testing Workflows- Creating effective testing workflows for comprehensive testing- Utilizing the Collection Runner for test execution- Introduction to Postbot for automated testing6. Advanced Testing- Contract Testing for ensuring API contracts- Using Mock Servers for effective testing- Maximizing productivity with Collection/Workspace templates- Integration Testing and Regression Testing strategies7. Automation with Postman- Leveraging the Postman CLI for automation- Scheduled Runs for regular testing- Integrating Postman into CI/CD pipelines8. Performance Testing- Demonstrating performance testing capabilities (showing the desktop client)- Synchronizing tests with VS Code for streamlined development9. Exploring Advanced Features - Working with Multiple Protocols: GraphQL, gRPC, and more Join us for this workshop to unlock the full potential of Postman for API testing, streamline your testing processes, and enhance the quality and reliability of your software. Whether you're a beginner or an experienced tester, this workshop will equip you with the skills needed to excel in API testing with Postman.
If finding errors in your frontend project is like searching for a needle in a code haystack, then Sentry error monitoring can be your metal detector. Learn the basics of error monitoring with Sentry. Whether you are running a React, Angular, Vue, or just “vanilla” JavaScript, see how Sentry can help you find the who, what, when and where behind errors in your frontend project. Workshop level: Intermediate
Cecilia Martinez, a technical account manager at Cypress, discusses network requests in Cypress and demonstrates commands like cydot request and SCI.INTERCEPT. She also explains dynamic matching and aliasing, network stubbing, and the pros and cons of using real server responses versus stubbing. The talk covers logging request responses, testing front-end and backend API, handling list length and DOM traversal, lazy loading, and provides resources for beginners to learn Cypress.
Testing Pyramid Makes Little Sense, What We Can Use Instead
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The testing pyramid - the canonical shape of tests that defined what types of tests we need to write to make sure the app works - is ... obsolete. In this presentation, Roman Sandler and Gleb Bahmutov argue what the testing shape works better for today's web applications.
Cypress is a powerful tool for end-to-end testing and API testing. It provides instant feedback on test errors and allows tests to be run inside the browser. Cypress enables testing at both the application and network layers, making it easier to reach different edge cases. With features like AppActions and component testing, Cypress allows for comprehensive testing of individual components and the entire application. Join the workshops to learn more about full circle testing with Cypress.
This Talk introduces Test Effective Development, a new approach to testing that aims to make companies more cost-effective. The speaker shares their personal journey of improving code quality and reducing bugs through smarter testing strategies. They discuss the importance of finding a balance between testing confidence and efficiency and introduce the concepts of isolated and integrated testing. The speaker also suggests different testing strategies based on the size of the application and emphasizes the need to choose cost-effective testing approaches based on the specific project requirements.
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