So far, we have covered almost everything about reactive programming using Spring 5.x. We have also looked at how to build a clean, asynchronous execution using Project Reactor 3 and how to use that knowledge for building web applications using WebFlux. Moreover, we learned how Reactive Spring Data complements the whole system, and how quickly we can upgrade our application to a cloud level one using Spring Cloud and Spring Cloud Streams.

In this chapter, we will finalize our knowledge base by learning how to test each component in our system. We will cover the testing techniques and utilities that help in the verification code, which is written using Reactor or any library that is compatible with the Reactive Streams specification. We will also look at features offered by the Spring Framework to test the reactive application from end to end.

In this chapter, we will cover the following topics:

• The demand for additional testing tools
• The essentials of Publisher testing using StepVerifier
• Advanced StepVerifier usage scenarios
• The tool set for end-to-end WebFlux testing