This chapter introduced us to the notion of reactive programming. We understood the concept of Observable events and reacting to them. This gave us an essence of what reactive programming is. After that, we went through reactive extensions and explored the API a bit. We saw how we can create Observables and subscribe to them. Finally, we looked at  an example that explained the way we can compose Observables using some operators available to us.
In next chapter, we'll cover one of the most important topics, that is, testing our programs. We'll go through the much talked about nowadays development model, that is, test-driven development (TDD). We'll start by answering the why and what of TDD and then understand the toolkits available in Scala for testing.
