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Introduction In this article, I will guide you on adding Jest (currently the most popular testing library) to test for projects using the NextJS framework. This integration helps developers automate the source code testing process, from logical functions (Unit Testing) to user interface testing (Integration Testing) in the Node.js environment. Here are the prominent advantages: Fast and effective: Jest runs tests in parallel, saving significant time as the project scales. Built-in Support: Next.js provides the next/jest configuration, making setup extremely simple, automatically handling CSS files, images, and framework-specific features. Excellent Watch Mode: Jest has the ability to detect recently changed files and only run related tests, keeping the development workflow smooth. Coverage Reports: This tool has built-in capability to statistic the percentage of source code tested, helping you assess application quality and reliability visually. Rich ecosystem: When combined with React...

Introduction Implementing testing in software development not only helps detect bugs early but also ensures system stability when performing upgrades or changing code. Testing helps programmers feel more confident, minimizes logic error risks, and creates a living document of how modules operate. In NestJS, we usually focus on three main concepts: Unit Test helps test each class or function independently End-to-End (e2e) Test tests the entire operation flow from request to response through a real server Test Coverage is an index measuring the percentage of source code that has been tested by test suites. Prerequisites In this article, I will continue to use the code from previous articles to implement tests; you can review those articles to get the source code to continue, or you can write similar tests based on the content according to your needs. Detail Update file package.json, focusing on the jest field { "jest" : { "moduleFileExtensions" : [ "j...