I have taken a lot of time to describe integration with MongoDB. However, testing persistence is one of the key points of automated tests, so it is very important to configure it properly. Now, we may proceed to the test's implementation. Spring Test provides support for the most typical testing scenarios, such as integration with other services through a REST client or integration with databases. We have a set of libraries available that allows us to easily mock interactions with external services, which is especially important for unit tests.
The following test class is a typical unit test implementation for a Spring Boot application. We have used the JUnit framework, which is the de facto standard for Java. The Mockito library is used here for replacing the real repository and controller with their stubs. Such an approach allows us to easily verify the correctness of every method implemented by the @Controller class. The test is performed in isolation from the external components...