End-to-end testing is essential to validate requirements, configurations, and functionality, especially in the age of DevOps and continuous delivery. It involves testing software or an application as it will be used by customers from start to finish, taking into account all dependencies and integrations. Effective end-to-end testing follows a seven-step process: defining scenarios, developing a testing environment, analyzing software and hardware requirements, defining how systems need to respond, designing test cases, running tests, and analyzing results. To measure the success of end-to-end testing, developers focus on deviations from the norm under different scenarios, ensuring proper outcomes and flagging any anomalies that need rework. Best practices for end-to-end testing prioritize common user scenarios, make tests realistic, and use error monitoring, unit tests, and integration tests first. However, there are challenges in end-to-end testing, such as complexity, workflow testing, and the need to test in client or production environments, requiring careful planning and pathway development.