Book Image

Kotlin Programming Cookbook

By : Aanand Shekhar Roy, Rashi Karanpuria
Book Image

Kotlin Programming Cookbook

By: Aanand Shekhar Roy, Rashi Karanpuria

Overview of this book

The Android team has announced first-class support for Kotlin 1.1. This acts as an added boost to the language and more and more developers are now looking at Kotlin for their application development. This recipe-based book will be your guide to learning the Kotlin programming language. The recipes in this book build from simple language concepts to more complex applications of the language. After the fundamentals of the language, you will learn how to apply the object-oriented programming features of Kotlin 1.1. Programming with Lambdas will show you how to use the functional power of Kotlin. This book has recipes that will get you started with Android programming with Kotlin 1.1, providing quick solutions to common problems encountered during Android app development. You will also be taken through recipes that will teach you microservice and concurrent programming with Kotlin. Going forward, you will learn to test and secure your applications with Kotlin. Finally, this book supplies recipes that will help you migrate your Java code to Kotlin and will help ensure that it's interoperable with Java.
Table of Contents (21 chapters)
Title Page
Copyright and Credits
Packt Upsell
Contributors
Preface
Index

Writing JUnit rules in Kotlin (@Rule)


Rules are a way to add functionalities that apply to all tests of the class. For example, ExternalResource executes the code before and after a test method. This can be used to set up a database, network, and filesystem connection before the test method, and can tear them down when the tests are complete. Of course, you can also do it using the @Before and @After annotations, but doing it with ExternalResource (as a JUnit rule) helps with code reuse.

Getting ready

I'll be using Android Studio 3.0 for coding.

How to do it…

In this recipe, we will be using ExpectedException as the JUnit rule because it helps the test declare that an exception is expected and also provides a way to clearly express the expected behavior. It is much more flexible than using the @Test(expected= ...) annotation because we can test specific error messages and custom fields.

In the following steps, we will learn how to write JUnit tests:

  1. Let's first create a simple method that throws...