How to Automate API Testing Using Postman Collections and Newman CLI

API testing fills a critical gap between unit tests and end-to-end UI tests by verifying that backend endpoints maintain their expected contracts, such as correct status codes, response shapes, and authentication. Postman allows developers to design HTTP requests and write JavaScript assertions directly within its interface, while Newman, Postman's official command-line runner, executes those collections outside the desktop app. Once a Postman collection is exported as a JSON file, Newman can run it via the terminal and generate HTML or JUnit reports without requiring Postman to be installed. The collection file can be stored in version control and integrated into CI/CD pipelines, such as GitHub Actions, enabling automated API tests to run on every push or pull request. The article demonstrates this workflow using httpbin.org, a public HTTP testing service, to simulate real requests without needing a private backend or custom infrastructure.