The site https://automationintesting.online is a free to use Web application that contains modern web technology to create a playground for you to practise a range of software testing skills. From UI and API automation to Exploratory and Accessibility testing, Automation in Testing online, offers you a safe space to practise your skills.
The web service deployed to https://restful-booker.herokuapp.com is a demo Web service that you can practise API testing and automation against. The web service contains multiple different method types and actions to practise with, all supported by in depth documentation for the API. It also comes with a series of bugs for you to find. Can you find the teapot?
The api-framework repository demonstrates a pattern to develop automated API checks using different languages and libraries to help you get started with automated API checking. There are runnable API checks that work against restful-booker app.
Selenium to Rest-Assured is a small library that can be used as an adapter to convert Cookies from Selenium to Rest-Assured and back to use in your automated checking.