End-to-end testing, also known as E2E testing, is a software testing technique that verifies the functionality and performance of an entire software application from start to finish under real-life circumstances. This type of testing approach starts from the end user’s perspective and simulates a real-world scenario. It ensures that all components work as expected and the software application functions correctly in real-world scenarios. End-to-end testing can be time-consuming because it takes a complete understanding of the product to write test cases. Companies often rely mostly on unit tests, snapshot tests, and integrations tests, and use end-to-end tests for only the highest priority user workflows. Automated testing tools like Selenium, Cypress, and Appium are commonly used for E2E testing to improve efficiency and accuracy. There are two types of end-to-end tests: horizontal and vertical. Horizontal E2E testing checks a specific layer or component works consistently across different parts of the software, while vertical E2E testing ensures a particular function works smoothly from the front-end interface down to the server and database. The purpose of E2E testing is to validate the application’s overall behavior, including its functionality, reliability, performance, and security.