Jest Framework

What is Jest Framework?

Jest is a JavaScript open-source framework mainly used for testing. Jest is majorly used to work with react-native based web applications and with react, and it mostly focuses on simplicity while doing any unit testing. Unit testing is often not very useful when run on the front end of any software because it is extensive and very time-consuming and raises complexity. But it can easily be removed using the jest framework. Also, the jest framework helps the programmer validate everything developed by using JavaScript, whether it is browser rendering of web applications or any mobile applications.

For automated browser testing, Jest plays a very important role. Jest is among the most famous JavaScript testing frameworks currently compared with other frameworks in existence. Along with this, Jest also provides a blended package of a built-in mocking library, an assertion library and a test runner. Its simplicity is mainly known for its simplicity, making it a unique tool for testing and building various JavaScript library projects such as Angular JS, Node JS, Vue JS, Babel, and Typescript.

Jest is a testing framework of JavaScript mainly designed to ensure the JavaScript codebase preciseness and accuracy. It helps us with the functionality to write tests with an approachable, familiar and feature-rich API ( Application Programmable Interface ) that will provide you results quickly for the code that we have written in it.

It is a well-defined document and requires little configuration, and can be extended whenever required to match out your requirements. Jest makes us do testing delightfully.

Jest is one of the most popular for testing react components. Initially, it was created by Facebook, especially for testing react applications. It makes it easier and faster to run JavaScript tests by having all needed things included in one framework. It mainly aims to work out of the box, configuration free and on most JavaScript projects.

It is very fast and safe; Jest can run all your tests parallel by ensuring they have a unique global state. To make things quicker and easier, it runs previously failed tests first and then reorganizes the runs of the next tests, which are based on the long test files.

Jest has a great toolkit available to programmers at one place itself, which is very well documented, properly maintained and well arranged in a good manner. It also helps to maximize the performance level by managing the tests in a parallel manner by running them in their processes. Jest also maintained the information coverage records, and from entire projects and various untested files, it collects code coverage information.

The jest framework tools have gained a lot of popularity, and this popularity led to the use of Jest for both JavaScript back-end and as well as for front-end applications. Various large companies - including Twitter, Pinterest, Instagram, etc.,- mainly for react testing uses Jest.

Jest itself is not a library, it is a JavaScript framework, and it does not rely on third-party tools for much functionality, as some competitors do. Anyone can use Jest, and it is a hassle-free part due to its zero-configuration Setup. You can easily install it, and from the beginning, you can write your very first test.

With the help of various mock functions API ( Application Programming Interface ), we can use mocked imports to observe various function calls with the easily readable syntax of any text.

Jest is very popular for unit testing and can be easily extended to include various integration tests. On the scale of different unit tests, automated tests are extremely contrary to end-to-end testing. There is too much software testing, which verifies different aspects of any mobile or web application, each operating on a different coating or layer and providing their unique type of feedback.

Unit testing is frequently cited as the most important among various types of software testing automated testing. Unit tests are mainly used to verify your application by breaking it into small parts in complete isolation. Also, unit tests ensure to provide more than the expected work.

As a result, unit testing is usually -

• It is quite fast to execute any test or application-based project.
• It is more or less easy to set up and does not require any elaborate configuration.
• It is very accurate in providing any feedback related to the project or any web and mobile application developed by the user.

Hence, unit testing is less realistic or imaginative because users usually do not interact with units under complete isolation.

Features of Jest Framework

1. Easy to set up - The jest framework is pretty simple to install on any system. You can directly install it by using the library named npm ( Node Package Manager ) or yarn. We can install the jest module globally using the' - g ' flag with an npm command line. Without setting up the package files for various npm tests, one can easily use the jest command directly by using the ' - g ' flag. It is very simple to use the jest framework; if you want to use the React-create app to create your react projects, we recommend that you do not need to do such things. The jest package consists of multiple modules, and there you can start writing tests immediately.
2. Performance and speed - The jest framework is very fast. It quickly executes all your test cases, efficiently and quickly without any delay, if your system performance is also good. Jest can save significant time from your test runs whenever your test is CPU bounded. Several factors make the Jest work fast and effectively -
   • Run that test first, which takes more time; due to this factor, all cores are utilized to the max.
   • Parallelization, due to this factor, all the tests are performed against several configurations simultaneously. Parallel testing is semi-automated testing that can simultaneously able to perform all tests against several configurations.
   • It catches babel transforms; here, babel is an open-source and free trans compiler of javascript.
3. Isolated working of all tests - Each jest test runs in its sandbox, which ensures that no two tests can interfere in between the working of another test or that it will not impact the execution of another test. However, we know that all tests are executing in system parallel. Still, the basic idea of isolation is to provide the environment of each test in such a way that it will consider running one at a time so that it could interfere with the working of other tests. By this property, the jest framework runs faster.
4. Powerful Mocking support - Before learning about this feature, we need to understand what exactly mocking is. Mocking is a technique to separate our various test subjects; this separation is done by interchanging the dependencies with objects, which can inspect and control. Whenever we talk about mocking in Jest, we typically discuss replacing dependencies with the mock functions. Jest support all types of Mocking; it can be followed as - timer mocking, functional Mocking, or mocking individual API ( Application Programming Interface ) calls.
5. Jest supports TypeScript - Jest support Typescript. We can implement it using the ts-jest package; as we all know, Typescript is used to develop JavaScript applications for both server-side execution and client-side execution. Typescript uses plain javascript, which is the most advantageous feature, and it is a very famous superset of javascript. The ts-jest package act as a typescript preprocessor along with the support of a source map for Jest, and It also has a very agile community.
6. Support snapshot testing - Snapshots testing has great use; it lets you capture a string representing your given or provided component and store it in a file. Snapshot testing is ideal for React Native and React applications, and for comparing the sequenced values of various other frameworks, you can use snapshots. By capturing the snapshots of the react component, greatly helps in validating the component's behaviour. You require to update your snapshot file if you want to change your UI ( User Interface ).

From all the above features and advantages of the jest framework, we can conclude that Jest is a very fast testing framework and very convenient and easy for us to install and set up a jest in our system. It is developed by Facebook and actively used by Facebook and many other users to test all the react applications and react based projects. It has convenient and frequently used packages, supports Typescript.

Basic Setup for executing any Test

Whenever we create a web or mobile application, we must test every feature and element of that application and its point of interaction with a user, which is quite mandatory. Web applications are consist of various modules and functions, which is mainly stated as the unit of code, and these units of code also need to be tested.

Two scenarios commonly arise in this situation:

• Inherit legacy code, and here legacy code refers to the older computer source code or the traditional code (base codes) that is already predefined for particular tests, that comes without tests because these codes have already been tested and do not require to undergo further tests.
• Implement a new functionality suddenly, in an unexpected way or manner.

For both the cases mentioned above, one must check whether the given functions produce the desired output.

For every test, there is a predefined flow in which, through following the flow step by step, our code is fully tested after undergoing till the end of the flow.

1. Initially, import the required function for a particular test.
2. Pass the necessary input into the chosen function.
3. Define the function's body so that it must produce the desired output after execution of the function.
4. At last check the working of function, whether it is resulting out the desired output or not.

Jest Installation Process

There are certain prerequisites and installation process of jest framework, which is necessary before writing your first test script with Jest. Such test script can also be a selenium test automation script.

So to run our jest tests scripts, we need to install some important libraries and packages, which is predefined set for to check particular test scripts.

• Node Package Manager (npm) and NodeJS: NodeJS can be installed directly by using the Windows Installer binary from the org website or by using the npm manager; node Package Manger is an open-source software library that over more than 8 lakhs code packages. Node Packaging Manager is a command-line tool generally used to update, install or uninstall various Node.js packages in our web-based or mobile applications.
  If you want to initialize the npm command, navigate the npm-command line tool, and install the latest version, you can easily apply the command as mentioned below.

• Selenium Web Driver: It is a web framework that allows you to run or implement cross-browser tests. It also permits you to choose any programming language that suits you for creating various test scripts. For automating mobile or any web-based application testing, a selenium web driver is used to verify whether the application performs expectedly or not. Jest module is installed in the root directory. Selenium web driver is a reliance for the jest module.
  By using the command line mentioned below, you can download the latest version of selenium WebDriver.

By using the command line as mentioned below, you can install the jest module using npm.

By using the Java - SDK jest keyword, testers will run the commands in the command line. Before further moving for the jest framework installation process, you must check whether your system must have already done with the installation process of Java Development Kit and configure the system with the JAVA environment; this is because Jest is a selenium test framework and selenium which is built on Java itself.

You can install the jest module globally using the flag ' -g ', and also, you can use the ' -g ' flag along with the npm command.

To use various Jest commands directly without setting up the package file for npm tests, you can do it easily by using the ' - g ' flag.

Let us understand more about the jest framework with the help of the example mentioned below-

Jest Example using package.json

If you want more information about test runs, use -verbose flag because Jest produces only rudimentary output by default.

If you want to run or execute one on one individual tests in a particular sequence, then you can use the npx jest test name command.

scripts :

Thus, testers can set up Jest to run various tests of a particular test directory for a specified test.

There are some procedural steps that you are required to follow before executing any test or program:

1. Initially, you all need to run the code
2. Evaluate the code you wrote earlier.
3. At last, start applying these codes, including some variations to make any web or mobile application, or you can make different websites.