Scala Test-Driven Development

Table of Contents

Scala Test-Driven Development

Credits

About the Author

Acknowledgments

About the Reviewer

www.PacktPub.com

Why subscribe?

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Errata

Piracy

Questions

1. Hello, TDD!

What is TDD?

Why TDD?

Changing our approach to problem solving

Iteratively writing failing tests

Baby steps

Brief introduction to Scala and SBT

What is Scala?

Why Scala?

Scala Build Tool

Why SBT?

Resources for learning Scala

Resources for SBT

Setting up a build environment

Steps for downloading and installing Scala

Steps for downloading and installing SBT

Creating a project directory structure

Build definition files

Hello World!

Creating a directory structure

Creating a build definition

Test first!

Summary

2. First Test-Driven Application

Testing frameworks

ScalaTest

A quick tutorial

Adding ScalaTest to the project

Choose your testing style

FunSuite

FlatSpec

FunSpec

WordSpec

FreeSpec

Spec

PropSpec

FeatureSpec

Resources for ScalaTest

Problem statements

IDE

Project structure

Write a failing test – RED

Writing application code to fix the test – GREEN

More tests – REPEAT

Intercepting exceptions

Summary

3. Clean Code Using ScalaTest

Assertions

Deliberately failing tests

Assumptions

Canceling tests

Failure messages and clues

Matchers

Matchers for equality

Matchers for instance and identity checks of objects

Matchers for size and length

Matching strings

Matching greater and less than

Matching Boolean properties

Matching number within ranges

Matching emptiness

Writing your own BeMatchers

Some more Matchers

Matchers for containers

Combining Matchers with logical expressions

Matching options

Matching properties

Checking that a snippet of code does not compile

Base test classes

Test fixtures

Calling get-fixture methods

Instantiating fixture-context objects

Overriding withFixture(NoArgTest)

Calling loan-fixture methods

Overriding withFixture(OneArgTest)

Mixing in BeforeAndAfter

Composing fixtures by stacking traits

Problem statement

Feature – decimal to hexadecimal conversion

BinaryToDecimalSpec.scala

HexadecimalToDecimalSpec.scala

DecimalHexadecimalSpec.scala

BeanSpec.scala

package.scala.packt

BaseConversion.scala

Summary

4. Refactor Mercilessly

Clean code

Red-Green-Refactor

Code smell

Expendable

Couplers

Modification thwarters

Bloaters

Object-oriented abusers

Obsolete libraries

To refactor or not to refactor

Doing it thrice (rule of three)

Adding new feature

Bug fixing

Code reviews

Refactoring techniques

Composing methods

Moving features between objects

Organizing data

Summary

5. Another Level of Testing

Integration testing

Functional testing

Acceptance testing

Need for user acceptance testing

Behavior-driven development

Introduction

Three amigos

Bird's-eye view of BDD

Gherkin

Executable specification

Don't repeat yourself

Talk is cheap

Adding Cucumber dependency

Directory structure

The feature file

Running the feature

Step definition

Summary

6. Mock Objects and Stubs

History

Coupling

Stubs

Mock objects

Expectations

Verifications

Fakes

Spy

Mocking frameworks

JMock

Advantages of JMock

EasyMock

Mockito

ScalaMock

Advantages of ScalaMock

mockFunction

Proxy mocks

Generated mocks

Let's dig a little deeper

Specifying expectations

Summary

7. Property-Based Testing

Introduction to property-based testing

Table-driven properties

Generator-driven properties

ScalaCheck

Generators

Generating case classes

Conditional Generators

Generating containers

Arbitrary Generator

Generation statistics

Executing property checks

Our own Generator-driven property checks

Summary

8. Scala TDD with Specs2

Introduction to Specs2

Differences between Specs2 and ScalaTest

Setting up Specs2

Styles

Unit specifications

Acceptance specification

Matchers

Simple Matchers

Matchers for strings

Matchers for relational operators

Matchers for floating point

Matchers for references

Matchers for Option/Either

Matchers for the try monad

Matching exception

Iterable Matchers

Matchers for sequences and traversables

Matchers for maps

Matchers for XML

Matchers for files

Matchers for partial functions

Other Matchers

Specs2 data tables

Running Specs2 tests

Summary

9. Miscellaneous and Emerging Trends in Scala TDD

Scala Futures and Promises

ExecutionContext

Futures

The Inside trait

The OptionValue trait

The EitherValue trait

Eventually

How to configure eventually

Simple backoff algorithm

Integration patience

Consumer-Driven Contracts

How services interface with each other

The gigantic way

Microservices

Using CDC to integrate microservices

Traditional way

Using CDC

Benefits of CDC

Summary

Scala Test-Driven Development

Scala Test-Driven Development

Copyright © 2016 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: October 2016

Production reference: 1211016

Published by Packt Publishing Ltd.

Livery Place

35 Livery Street

Birmingham 

B3 2PB, UK.

ISBN 978-1-78646-467-5

www.packtpub.com

Credits

About the Author

Gaurav Sood is a Scala and XQuery consultant who consults through his own company Omkaar Technologies Limited. He started playing with computers at a very early age and eventually went onto complete his post-graduate degree in computer sciences. 

After working for an Indian software service house for a couple of years, he decided to start his own consultancy business. Since then, his company has provided services to a few Tier 1 Investment banks, the government of the United Kingdom, and publishing houses. He has gained an irrefutable reputation and distinction in the industry. Gaurav has previously worked with HSBC, Deutsche Bank, Reed Elsevier, Lexis Nexis, John Wiley & Sons, HMRC, and Associated News, amongst other smaller names in the industry.

When he is not consulting or writing, Gaurav can be seen making a fuss of his family. He likes spending time with his beautiful wife and two sons. He also loves volunteering for charity fund raising through sponsored runs. Gaurav also runs a small charitable trust in Shimla, India (New Life), which helps provide education to under-privileged children.

Acknowledgments

I would like to start by thanking God for the courage and determination to write this book. There are many people I would like to express my gratitude to, for helping me with this book. These people have seen me through this book, provided support, offered comments, proofread my work, and been a critic when I needed one.

I want to thank my family for being my strength, my parents, Satish and Brij, wife, Khushboo, and two little boys, Johan and Jairus, who have been my strength. They have supported and encouraged me in spite of all the time it took me away from them. It was a lingering and arduous voyage for them. I would also like to thank my in-laws, Hardeep and Kawaljit, along with my siblings and friends for encouraging me to consider writing this book. They have always believed in me.

I would also like to thank Packt Publishing, their extremely helpful editorial staff and technical reviewers for enabling me to publish this book and encouraging me every step of the way. I would also like to thank Artima Inc, for their permission to refer to their work.

Special thanks once again to my lovely wife Khushboo. Without you, this book wouldn’t have been possible.

Last but not the least: I beg forgiveness to all those who have been with me over the years and whose names I have failed to mention.

About the Reviewer

Román García has been a self-taught software engineer for the last two decades, and is currently CTO at Fravega.com, one of the biggest retail companies in Argentina where he resides. Previously, he worked as a software architect for Despegar.com, ZonaJobs.com, DeRemate.com, and others. An avid cowboy programmer, he is passionate about software development, clean code, test-driven development, and madly in love with the Scala programming language.

I’d like to thank my parents for all their support during the early years, when I found my passion for programming, and, last but not least, to my loving wife, Elisabeth, and my two kids, Manuela and Joaquin, for all the love they brought to my life.

www.PacktPub.com

For support files and downloads related to your book, please visit www.PacktPub.com.

Did you know that Packt offers eBook versions of every book published, with PDF and ePub files available? You can upgrade to the eBook version at www.PacktPub.com and as a print book customer, you are entitled to a discount on the eBook copy. Get in touch with us at [email protected] for more details.

At www.PacktPub.com, you can also read a collection of free technical articles, sign up for a range of free newsletters and receive exclusive discounts and offers on Packt books and eBooks.

https://www.packtpub.com/mapt

Get the most in-demand software skills with Mapt. Mapt gives you full access to all Packt books and video courses, as well as industry-leading tools to help you plan your personal development and advance your career.

Why subscribe?

Fully searchable across every book published by Packt

Copy and paste, print, and bookmark content

On demand and accessible via a web browser

Preface

Test-Driven Development (TDD) goes hand-in-hand with Agile practices, which is gradually becoming the undisputed standard process or delivering quality software on time. The TDD process originated from the need to better understand and refine the requirements for a system.

Scala has gradually, despite all apprehensions, made a niche for itself as the language of choice for delivering modern versatile systems and microservices. It is slowly and steadily replacing the conventional object-oriented models with more robust and immutable functional constructs. The popularity of Scala emanates from the fact that it provides a bridge for developers to make a transition from the object-oriented to the functional world.

Scala, like all other languages, can allow developers to get so engrossed in its intricacies and magic that the real purpose of the application can easily get lost in over-engineering. Therefore, TDD is required to keep the application code tightly tied to the requirements.

What this book covers

Chapter 1, Hello, TDD!, contains a brief introduction of TDD and Agile process. We discussed the benefits of TDD and how and why it needs to be used.

Chapter 2, First Test-Driven Application, creates our very first working application using TDD. The purpose of this chapter is to provide a quick win and give a taste of what lies ahead.

Chapter 3, Clean Code Using ScalaTest, discusses some of the principles of clean code and delves into the ScalaTest framework.

Chapter 4, Refactor Mercilessly, discusses various refactoring techniques and their benefits. The idea is to build a gradual appreciation of the refactoring process.

Chapter 5, Another Level of Testing, discusses the concepts of functional testing and behaviour-driven development.

Chapter 6, Mock Objects and Stubs, takes an in-depth look into the mocking frameworks that can be used with ScalaTest and Specs2 to enable mocking out the dependencies during testing.

Chapter 7, Property-Based Testing, discusses the techniques of writing tests that are driven from inputs provided in the form of tabular data or that is randomly generated.

Chapter 8, Scala TDD with Specs2, looks at an alternative testing framework for test-driving Scala code. We also compare ScalaTest and Specs2 so the reader can make an informed choice.

Chapter 9, Miscellaneous and Emerging Trends in Scala TDD, explores some new techniques, features, and processes that may soon become incorporated into the mainstream application development process.

What you need for this book

The following software is recommended for use with this book:

Scala

SBT

IntelliJ or Eclipse IDE

Who this book is for

This book is for Scala developers who are looking to write better quality and easily maintainable code. No previous knowledge of TDD/BDD is required.

Conventions

In this