Modern full-stack applications often require a backend service to support frontend data rendering, and testing these applications can be challenging without replicating backend setups. This tutorial introduces Nock, a Node.js library for mocking HTTP requests, allowing developers to test API endpoints without making actual calls, thus speeding up test execution. By integrating Nock with a continuous integration pipeline, developers can automate API tests, simulate responses, and manage test environments effectively, ensuring applications handle various scenarios without relying on real external services. The tutorial demonstrates using Nock with a sample todo application, highlighting the benefits of mock testing, such as reduced strain on external resources and faster test times, while also covering how to bypass mocks for real endpoint verification. Additionally, it provides guidance on setting up a CI pipeline with CircleCI, emphasizing the importance of clearing mocks after tests to prevent interference and ensuring successful automated test execution, ultimately enhancing testing efficiency and reliability.