Spock: Up and Running

Chapter 16. Test Driving an RxJava Application

In this chapter, we work through an example of test driving an implementation. We’re going to implement a class that polls for new messages on a user’s Squawker timeline and then hands them off to another component for processing. We could use this as the core of a simple command-line client, a desktop GUI application, or a websocket-based browser application.

For the implementation we’ll use RxJava.

RxJava

RxJava is an implementation of the reactive streams pattern for the JVM. It was first developed as an open source project by Netflix.

If you’ve looked at some of the API extensions added in Java 8, stream processing will be familiar to you. If not, don’t worry too much. The point of this chapter is to provide an example of test driving a solution with the implementation following a failing test. We won’t be using any particularly complex RxJava code and won’t be getting into advanced reactive streams topics such as backpressure.

It will be helpful for you to be familiar with the Java 8 concept of a function type and the syntax for lambdas and method references.

Before starting, let’s consider what we mean by “test-driven development” and what a test-driven development (TDD) workflow looks like.

Rather than trying to implement the entire solution at once, either before or after its tests, we’ll work iteratively. Each iteration involves deciding on a feature or behavior to implement next, writing a failing test, implementing the ...