JUnit (https://junit.org/junit5/) is the most widely used Java testing framework. It is a free and open source software. It was originally intended for unit testing but combined with Spring Test Framework (https://docs.spring.io/spring/docs/current/spring-framework-reference/testing.html#testing-introduction) it can also be used for Integration testing. JHipster creates unit tests and REST API integration tests using JUnit and Spring Test Framework.