Unlocking the Power of Testing in React Applications
Testing is an essential practice in software engineering that helps build robust and high-quality software, boosting a team’s confidence in the code and making the application more flexible and prone to fewer errors. In this article, we’ll delve into the world of testing React applications using Jest and React Testing Library, a popular combination of a JavaScript testing framework and a React utility for testing components.
What is Testing?
Testing is the process of automating assertions between the results the code produces and what we expect the results to be. When testing React applications, our assertions are defined by how the application renders and responds to user interactions.
Introduction to Jest and React Testing Library
Jest is a JavaScript testing framework that allows developers to run tests on JavaScript and TypeScript code and integrates well with React. It’s a framework designed with simplicity in mind and offers a powerful and elegant API to build isolated tests, snapshot comparison, mocking, test coverage, and much more.
React Testing Library is a JavaScript testing utility built specifically to test React components. It simulates user interactions on isolated components and asserts their outputs to ensure the UI is behaving correctly.
React Testing Library vs. Jest
React Testing Library is not an alternative to Jest. Each performs a clear task, and you need them both to test your components. Jest is a test runner that finds tests, runs the tests, and determines whether the tests passed or failed. Additionally, Jest offers functions for test suites, test cases, and assertions. React Testing Library provides virtual DOMs for testing React components.
Setting Up Your Testing Environment
To set up your testing environment, you’ll need to install Jest and React Testing Library. The easiest way to get a React application up and running is by using create-react-app. You can also clone the tutorial project from GitHub.
Building a React Application for Testing
Next, let’s build a minimal application that will display users from an API. We’ll use the JSONPlaceholder user API. This app is built exclusively for building tests.
Building a Unit Test
Unit tests test individual software units or components in isolation. A unit could be a function, routine, method, module, or object, and the test objective determines if the unit outputs the expected results for a given input.
Testing Components with Jest
Testing components is not much different than testing functions. The idea and concepts are the same, but the difference is in how we write the assertions. We will test our App component by building a few test cases, and on each test case, we will introduce different things we can do to validate React components.
Mocking with React and Jest
Our next step is to validate how the component will react to the data gathered from the API. But, how can we test the data if we are not sure what the API’s response would be? The solution to this problem is mocking.
Snapshot Testing
Snapshot tests are useful when you want to make sure your UI does not change unexpectedly. A typical snapshot test case renders a UI component, takes a snapshot, then compares it to a stored reference snapshot file.
Which Testing Library is Best for React?
When it comes to testing libraries or frameworks, there are various options and combinations to consider. Here’s a look at some of the most popular testing frameworks and their specific pros and cons: Jest, Enzyme, React Testing Library, Jasmine, and Mocha.
Get Started with Testing Your React Application
Testing your React application is the key to producing high-quality apps, and thanks to React, Jest, and React Testing Library, it’s easier than ever to test our components and applications.