Mockoon is the easiest and quickest way to design and run mock REST APIs.

Datadog is a cloud-based monitoring and analytics platform that provides observability and security for cloud-scale applications

Postman is an API platform for building and using APIs. Postman simplifies each step of the API lifecycle and streamlines collaboration so you can create better APIs—faster.

Puppeteer is a Node.js library which provides a high-level API to control Chrome/Chromium over the DevTools Protocol.

API Testing Platform that automatically generates unit test cases with dependency mocks from API calls

Testing and validating REST services in Java is harder than in dynamic languages such as Ruby and Groovy. REST Assured brings the simplicity of using these languages into the Java domain.