Ensuring comprehensive test coverage is essential to instill confidence in the quality of your web application. To achieve this, you can leverage powerful tools such as Jest and React Testing Library that simplify the process of writing and executing tests.
By leveraging the capabilities of Jest and React Testing Library, which are conveniently integrated with Create React App, you can establish a solid testing foundation for your web application. These tools adhere to the principle that testing should mirror real-world usage, allowing you to build test suites that accurately reflect how users interact with your software. With their combined power, Jest and React Testing Library enable you to achieve extensive test coverage and confidently deliver high-quality applications that meet user expectations.
What is Testing?
Let’s gain a better understanding of testing. The term “testing” encompasses various aspects, including manual testing, unit testing, regression testing, integration testing, load testing, and more.
Test-Driven Development (TDD) encourages writing tests and expected outcomes before implementing the logic of a method. Initially, the test will fail. Then, you work on making the method pass the test. Once it passes, you can refactor the code to improve its readability, performance, or other aspects. As long as the test continues to pass, you can be confident that your refactoring didn’t introduce any regressions.
By writing your own unit tests, you put yourself in the mindset of someone using the methods, which often helps identify new checks, validations, and bugs. Additionally, it may lead to design changes that make the code more testable, such as decoupling components to enable focused testing of each individual unit.
Let’s delve into the different types of tests that can be implemented:
- Unit tests: Unit tests focus on testing individual units or components of the software. These units can be functions, methods, procedures, modules, components, or objects. The purpose of unit testing is to isolate and verify specific sections of code to ensure they perform as expected. It involves testing individual modules, functions, or components to validate their proper functionality. For example, unit testing verifies whether a function, statement, or loop in a program works correctly.
- Snapshot tests: Snapshot tests are designed to prevent unexpected changes in a web application’s user interface (UI). They capture the code of a component at a specific point in time, allowing for comparison against other potential states it may assume. In a snapshot test scenario, a UI component is rendered, and a snapshot is taken. This snapshot is then compared to a reference snapshot file stored with the test. If the two snapshots differ, the test fails, indicating either an unexpected change or the need to update the reference snapshot to reflect the new UI component.
- End-to-end tests: End-to-end tests automate a browser to ensure that an application functions correctly from the user’s perspective. These tests simulate real user interactions and verify that the application works seamlessly as a whole. End-to-end tests save time by allowing them to be executed repeatedly once they are written. Running a suite of hundreds of end-to-end tests can significantly reduce the effort compared to writing tests for each individual unit. However, end-to-end tests can be time-consuming and challenging to debug, presenting some challenges in their implementation.
Understanding and implementing these different types of tests allows for comprehensive testing coverage, ensuring the reliability and functionality of front-end applications.
What is Jest?
Jest, a JavaScript testing framework, offers a delightful testing experience with its emphasis on simplicity. It can be easily installed using npm or Yarn. Jest falls under the category of test runners, providing a comprehensive set of utilities. While it is commonly used for testing React applications, its versatility extends beyond React.
Enzyme, on the other hand, is a library specifically designed for testing React applications. Its primary focus is on testing React components, allowing developers to write assertions that simulate actions and verify the correctness of the user interface (UI).
Features of Jest
Jest, as a comprehensive and robust testing framework, stands out from other automated testing frameworks due to its exceptional range of features. Let’s explore some of the key features that make Jest an outstanding choice for developers:
- Fast Execution: Jest excels in speed, enabling developers to streamline their testing process by quickly executing test cases.
- Efficient Watch Mode: With Jest’s watch mode, users can efficiently analyze the impact of specific changes on the overall test suite output, providing valuable insights during development.
- Pre-commit Hooks and Snapshot Tests: Jest offers pre-commit hooks that help developers reduce the number of tests executed by a test suite. Snapshot tests, a popular feature of Jest, efficiently reduce the effort required for regression testing, thereby enhancing the overall testing process.
- Flexibility and Built-in Support: Jest provides built-in modules that offer excellent support for plugins. This eliminates the need to rely on third-party executables like Mocha or Cucumber for specific activities. Jest’s easy configurability and seamless compatibility contribute to its popularity among developers.
- Advanced Features: Jest offers a range of advanced features, including auto-mocking modules, coverage thresholds, and mappers. These features enhance the efficiency and effectiveness of testing processes.
- Support for Multiple Projects: Jest supports multiple projects within the same runner, enabling developers to handle multiple projects efficiently within a unified testing environment.
With its exceptional features, Jest empowers developers to conduct comprehensive and efficient testing, making it a top choice in the development community.
React Testing Library
React Testing Library (react-testing-library) has been a pivotal discovery in our testing journey, greatly influencing our approach. This library, designed to work seamlessly with Jest, challenges us to think critically about the essence of our tests. In the past, our team grappled with finding the right balance between test coverage and effectiveness.
While testing individual components holds importance, testing the cohesion and interaction among these components becomes even more crucial. After all, end users are concerned with the seamless functionality of the app, not its internal structure or underlying technology.
By emphasizing integration tests and user-centric testing, React Testing Library reshapes our testing perspective, enabling us to create more robust and meaningful tests that truly validate the user experience.
How can JEST be used for unit testing React Apps?
Step 1: Create a new React app
To perform unit testing on a React app, start by creating a new app using the following command:
npx create-react-app react-testing-tutorial
When using create-react-app to create a React project, Jest and React Testing Library are already included by default, so there’s no need to install them manually.
Step 2: Create a component
Create a component called “Counter” that increments and decrements a numeric value when respective buttons are clicked.
Step 3: Write a unit test for the React component
Follow these steps to write a unit test for the React component:
- Create a test block.
- Render the component in a virtual DOM.
- Select the elements you want to interact with.
- Interact with the elements.
- Assert the expected results.
Step 4: Run the test
Run the test using the command:
npm run test
The test results will be displayed, indicating whether the unit test passed or not.
Setup and Teardown
To ensure proper setup and teardown for each test, it is common practice to render the React tree to a DOM element that is attached to the document. This allows the tree to receive DOM events. At the end of the test, it is important to clean up and unmount the tree from the document to maintain test isolation.
One approach to achieve this is by using beforeEach and afterEach blocks. These blocks are executed before and after each test, ensuring that the necessary setup and cleanup steps are performed for each individual test.
Renderig
In order to verify if a component renders correctly with given props, it is common to perform tests. This test ensures that the component is rendered correctly with different name props. It uses the render function from react-dom to render the component into the specified container. The act function from react-dom/test-utils is used to wrap the rendering and assertion code. After each test, the component is unmounted and the container is cleaned up.
Code coverage
To measure the extent to which your code has been executed during testing, you can utilize code coverage analysis. In Jest, generating code coverage reports is straightforward.
Executing either of these commands will trigger the test suite and produce a detailed code coverage report. Jest will instrument your code to track which lines, functions, and branches have been executed during the test execution. The generated report will include metrics such as statement coverage, branch coverage, function coverage, and line coverage, allowing you to assess the overall quality and completeness of your test suite.
You may perform Jest testing on a bigger scale with the help of cloud-based digital experience testing platform like LambdaTest on an online browser farm with over 40 different operating systems and browsers. You can perform automation testing using Jest framework across 3000+ real browsers, devices and OS combinations.
Data Fetching
Instead of making real API calls in all of your tests, you can simulate requests by using dummy data. Mocking the data fetching process with fabricated data helps prevent unreliable tests caused by an unavailable backend and speeds up the test execution. It’s important to note that while using mock data is advantageous, running a subset of tests with an “end-to-end” framework can still be valuable for assessing the seamless integration and functionality of the entire application.
Mocking Modules
When working with testing environments, there are situations where certain modules may not perform as expected or may not have a substantial impact on the actual test being conducted. In order to streamline the process of writing tests for your own code, it can be beneficial to substitute these modules with mock versions that offer simulated functionality.
Mocking modules involves creating replacements for the original modules that mimic their behavior in a controlled manner. These mock modules are specifically designed for testing purposes and allow you to isolate the code under test from its dependencies. By substituting complex or external modules with simpler, dummy implementations, you can focus on testing the logic and functionality of your code in a more controlled and predictable manner
Conclusion
Unit testing is the simplest technique to improve the quality of your React applications because it aids in the detection of bugs and faults in your code. Additionally, because less time is spent on bug repair in the later stages of the project, early bug discovery in the SDLC lowers the overall cost of development. This increases general consumer satisfaction and aids in attracting more reliable customers.
Once the unit testing is complete, it is advised to test the application from beginning to end on real devices and browsers to spot any user experience bottlenecks. You are able to test on more than 3000 browser device combinations under actual user circumstances by using a real device cloud, such as LambdaTest.
