Jest has become one of the most popular test runners in recent years, particularly for projects that use React. Its popularity is due in part to its ease of use and flexibility, as well as its ability to handle complex testing scenarios with ease. It is highly configurable, allowing you to customize your test suite to meet the specific needs of your project.
What is Jest?
The creator of Jest, Christoph Nakazawa, developed it with a focus on supporting and simplifying testing for large web applications. The framework is highly configurable and includes a wide range of tools and features that make it easy to write and run tests for complex web applications.
It includes built-in support for features like snapshot testing and mocking, which can be challenging to implement with other testing frameworks. Snapshot testing allows developers to compare the output of a component to a previously saved version to ensure that it has not changed unexpectedly while mocking makes it easy to simulate the behavior of external dependencies.
Keynote Features of Jest
Jest is a comprehensive and powerful testing framework that offers a wide range of features that are unmatched by other automated testing frameworks.
- Jest’s speed of execution is one of its most notable features, which makes it an ideal choice for developers who want to streamline their testing process.
- Jest’s watch mode is also highly efficient, as it allows users to analyze how specific changes impact the overall output of the test suite.
- It offers pre-commit hooks, which can help developers reduce the number of tests performed by a test suite. These snapshot tests are a popular way of reducing regression testing efforts, which can greatly improve the efficiency of the testing process.
- Jest is also highly flexible, as it provides built-in modules that offer excellent support for plugins, which eliminates the need to download third-party executables like Mocha or Cucumber for specific activities. This, coupled with its easy configurability and lack of compatibility issues, makes Jest a highly popular choice among developers.
- Moreover, migrating a current test project to Jest is easy, thanks to the code mods module.
- Jest offers advanced features such as auto-mocking modules, coverage thresholds, and mappers, which allow for more efficient testing. Jest also supports multiple projects in the same runner, which can greatly improve the efficiency of the testing process.
Advantages of Jest
- Zero Configuration
One of the most significant advantages of Jest is that it requires zero configuration. It provides a pre-configured setup for unit testing with features like code coverage, test execution reports, and much more, making it easy to get started with testing.
Jest’s snapshot testing feature allows developers to compare current test results with previously saved ones, making it easier to track any unexpected changes. It also helps reduce the time and effort required for manual testing.
- Fast and Safe
Jest’s ability to run tests in parallel saves a lot of time and reduces repetition. In addition, it prioritizes the failed tests, ensuring that they run first, and then queues up the remaining tests based on their execution time, making testing faster and more efficient.
- Documentation and Support
Jest has excellent documentation that is easy to follow and includes real-life examples, making it easier for developers to understand how to use the framework. Additionally, the Jest community is very active, providing excellent support over Discord, making it easier for developers to troubleshoot issues and find solutions.
- Easy Mocking
Jest makes it simple to mock any object that is out of scope, allowing developers to test their code more effectively. The framework comes with a Mock Functions API that allows developers to spy on function calls and test them more efficiently.
- Code Coverage for Tests
Jest provides developers with a simple way to get code coverage for their tests. It offers a –coverage command that requires no additional setup, making it easier for developers to analyze their code’s test coverage. It also provides coverage reports for untested cases, allowing developers to identify areas that need more testing.
In summary, Jest’s many advantages, including zero-configuration, snapshots, excellent documentation, fast test execution, easy mocking, and code coverage, make it a popular choice among developers looking for an efficient and powerful testing framework.
Prerequisites for installation of Jest
- To begin with, you need to install the Java Development Kit (JDK 7.0 and above), which is essential for Selenium automation testing scripts. This requirement is due to the fact that the Jest framework employs Selenium, which is a popular automation testing tool for web applications. You can download the JDK from its official website and install it on your system.
- Finally, you need to install a browser driver, which is used to implement Selenium WebDriver’s protocols. Browser drivers assist in converting commands given by the Selenium WebDriver into a browser’s native API. This enables the WebDriver to interact with the web page and automate testing. Therefore, before running Jest scripts, you must install the appropriate browser driver for the browser you plan to use in your testing.
When developing a web application, it is crucial to test every aspect, including features, elements, and user interaction points. Additionally, units of code such as functions and modules also require testing. There are two scenarios that are common in this situation: inheriting legacy code without tests or implementing a new feature. In both cases, it is necessary to verify if a given function produces the expected result. Here is an example of a typical test flow:
- Import the function that needs to be tested
- Provide input to the function
- Define the expected output
- Verify if the function produces the desired output
Jest Vocabulary: Mock
A mock in Jest is a tool that simplifies testing connections between different pieces of code by replacing the actual implementation of a function. Instead, it captures the function’s calls and the parameters passed in those calls.
This code snippet defines the behavior of the mock and replaces the actual implementation of the function with this behavior. As a result, when the function is called during testing, the mock function is executed instead of the original function.
Using mocks in Jest can help us isolate the specific behavior of a function or module, making it easier to test. By mocking dependencies, we can test how our code behaves when certain conditions are met without actually calling external resources.
Jest provides several functions to create and manage mocks, such as jest.fn(), jest.mock(), and jest.spyOn(). These functions allow us to create different types of mocks and set expectations for how they should be called and with what parameters.
Overall, using mocks is a powerful technique to make testing more efficient and effective, as it allows us to focus on the behavior of our code without worrying about external dependencies or complex setups.
- Learning Jest can be a bit challenging for those who are accustomed to using other testing libraries. Since Jest has its own set of features, functions, and syntax, it may take some time for developers to get familiar with it. This can lead to a slower learning curve and initial difficulty in writing Jest tests.
- Another potential limitation of Jest is that it may not be fully compatible with all integrated development environments (IDEs). This means that developers who use unsupported IDEs may not be able to access powerful features like IntelliSense and auto-import. This can be a major disadvantage for developers who rely heavily on these features to streamline their workflow.
- Compared to other similar libraries, Jest may also lack sufficient library and tooling support. Developers who require a wide range of libraries and tools to test their code may find that Jest does not offer the same level of support as other testing frameworks.
- Finally, the auto-mocking feature in Jest can make it slower than other testing libraries. This is because Jest automatically creates mock versions of any dependencies, which can take time to set up and run. While this feature can be useful in specific scenarios, developers should be aware that it may impact the overall performance of their testing process.
To overcome many of its limitations, Jest cloud grids, such as LambdaTest, provide you with the ability to carry out Jest testing on a larger scale. With LambdaTest, you can automate cross-browser testing on a browser farm that offers over 40 browsers and operating systems, allowing for the scalability of test execution. This ultimately leads to better test coverage and product quality.
To run your first Jest automation testing script online, simply visit the LambdaTest. With a free sign-up, you can enjoy your first 100 Jest automation testing minutes on us. Additionally, you can access the lifetime benefits of manual cross-browser testing, responsive testing, and more through LambdaTest, the world’s fastest-growing cloud Jest Grid.
LambdaTest’s comprehensive Jest tutorials will help you develop a better functional understanding of the Jest framework. By running your first Jest test script on the LambdaTest cloud, you can kick-start your Jest automation journey without worrying about the challenges of Jest infrastructure.