In this chapter, we learned how to test asynchronous code written using Reactor 3 or any Reactive Streams-based libraries. In turn, we covered the essential points of testing reactive Spring applications, based on the WebFlux module and the Spring Test module. Then, using WebTestClient, we learned a way to verify a single controller in isolation, or the whole application with mocked external interaction. Furthermore, we learned knowing how to test Reactor 3 helps us in testing the whole system in integration. Along with everyday business logic checking, we learned a few tips for working with mocked security, which is also a crucial part of modern web applications. Finally, this chapter ended with some tips and tricks for WebSocket testing. Here, we saw some of the limitations of the 5.0.x Spring Test module. Nevertheless, by adopting WebSocketClient, we learned how to build a testable data flow and check the correctness of the client-server interaction. Unfortunately, we also discovered that there is no simple way to mock WebSocketClient for a server-to-server interaction.

Since we have finished testing our system, it is time to learn how to deploy a web application to the cloud and learn how to monitor it in production. Consequently, in the next chapter, we will cover how to work with Pivotal Cloud, the toolset that helps us to monitor the entire reactive system. We will also cover how Spring 5 helps us to solve problems.