End-to-end testing, often abbreviated as E2E testing, is a testing approach that validates the complete workflow of an application from start to finish. Its main goal is to ensure that every part of the system works together as expected, simulating real user behavior. In E2E testing, you interact with your application just as a user would—by clicking buttons, filling out forms, and navigating between pages. This type of testing checks not only the user interface but also how the frontend and backend communicate, ensuring that all integrated parts work seamlessly.

E2E testing is different from unit and integration testing:

• Unit testing focuses on individual functions or components in isolation, verifying that each piece works correctly on its own;
• Integration testing checks how different parts of the application work together, but usually only a few modules at a time;
• In contrast, E2E testing covers the entire application stack, from the user interface down to the database, and verifies that the whole system responds correctly to real-world scenarios.

In React applications, E2E tests typically cover scenarios such as:

• User registration and login flows;
• Form submissions;
• Navigation between pages;
• UI validation.

You might write an E2E test to ensure that a user can successfully add an item to a shopping cart, proceed to checkout, and receive a confirmation message. These tests help catch issues that might not be visible when testing components or functions in isolation, such as problems with routing, authentication, or network requests.