Daniel Hinojosa - Testing in Scala

This book enhances the Scala language with standard test-driven development practices, highlighting the best testing tools today. This book will cover both the ScalaTest and the Specs2 testing frameworks, which help you create quick and easy tests. Testing is also often the most overlooked aspect of introductory programming language books. This book is dedicated to mending that gap.

We will run all these tests using Simple Build Tool (SBT). SBT is similar to some earlier build tools and competitors: Maven, Gradle, and Buildr. What makes SBT highly attractive is its ease of use and the small size of the build file. Type a few lines of code for your build file and youre off and running on your project. We will also cover SBTs wonderful triggered execution feature, which complements test-driven development by building and testing code whenever a file is saved.

ScalaTest and Specs2 are two of the most dominant testing frameworks for Scala around today. Each framework has a different intent and goal, but they share the same ideal of making testing concise, and they both leverage the Scala programming language to make testing easy and fun. Testing frameworks are nothing new, of course, and have been used with other programming languages for years. Those familiar with other programming languages and their testing tools will find some similarities with Scalas current testing tools. ScalaTest and Specs2 borrowed ideas from Cucumber. But upon these shoulders of giants, Scala testing systems have also stepped out on their own and created some of the most mind-blowing testing tools found in any language.

Testing in Scala will also illustrate mocking code, so as to keep our tests isolated from large subsystems and networks. Mocking is, in essence, creating a substitute for various objects to isolate tests from volatile elements of their environment (such as the contents of databases) and to help unit tests run fast. This book shows how you can use Scala with Java-based mocking frameworks that have been used for years by Java programmers, EasyMock and Mockito. We will also introduce you to a new framework, ScalaMock. Formerly known as Borachio, ScalaMock was inspired by Javas EasyMock and Mockito but takes their work further, even offering support for mocking final classes and Scala objects.

Following mocking, we will also generate a massive battery of prefabricated test data using Scala Check, which is borrowed heavily from the Haskell programmed testing framework called QuickCheck. Scala Check has preconfigured formulas to generate strings, numbers, and other various objects automatically. Scala Check also offers formulas to generate your own custom test objects.

This book will be organized in a TDD fashion: test first, fail; test again, succeed maybe; test again, succeed, and so on.

Because Scala is a deep forest of coding possibilities, my intent is to start on familiar ground, with the imperative programming paradigm, and work our way to the Scala functional programming paradigm, discovering some things about functional programming along the way. I will describe some Scala calls that may be obscure, either to introduce you to some constructs that you may not be familiar with, or as a refresher for those that are familiar with Scala.