Test-Driven Python Development

Siddharta Govindaraj

• Publisher: Packt Publishing
• Year: 2015
• ISBN:
  9781783987931
• Topic: Informatik
• Subtopic: Programmierung in Python

About This Book

• Write robust and easily maintainable code using the principles of test driven development
• Get solutions to real-world problems faced by Python developers
• Go from a unit testing beginner to a master through a series of step-by-step tutorials that are easy to follow

Who This Book Is For

This book is intended for Python developers who want to use the principles of test-driven development (TDD) to create efficient and robust applications. In order to get the best out of this book, you should have development experience with Python.

Test-Driven Python Development

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Table of Contents

Test-Driven Python Development

Credits

About the Author

Acknowledgments

About the Reviewers

www.PacktPub.com

Support files, eBooks, discount offers, and more

Why subscribe?

Free access for Packt account holders

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. Getting Started with Test-Driven Development

Prerequisites

Understanding test-driven development

TDD versus unit testing versus integration testing

Using TDD to build a stock alert application

Writing our first test

Analyzing the test output

Test errors versus test failures

Making the test pass

Reorganizing the test code

Running the tests after the reorganization

Summary

2. Red-Green-Refactor – The TDD Cycle

Tests are executable requirements

Arrange-Act-Assert

Documenting our tests

Testing for exceptions

Exploring assert methods

Specific asserts versus generic asserts

Setup and teardown

Brittle tests

Refactoring the design

Refactoring tests

Exploring the Rule classes

Exercise

Summary

3. Code Smells and Refactoring

A dual crossover moving average

Implementing the dual crossover moving average

Identifying code smells

Refactoring

The Rename Variable and Rename Method refactorings

Commenting Styles

Replace Magic Literals with Constants

The Extract Method refactoring

Replace Calculation with Temporary Variable

Extract Conditional to Method

The DRY principle

Single Responsibility Principle

Extract Class

Move Method to Class

The importance of tests

Exercise

Wrapping up

Summary

4. Using Mock Objects to Test Interactions

Hand writing a simple mock

Using the Python mocking framework

Mocking objects

Mocking return values

Mocking side effects

How much mocking is too much?

Mocks versus stubs versus fakes versus spies

Patching methods

An important gotcha when patching

Tying it all together

Summary

5. Working with Legacy Code

What is legacy code?

Understanding the code

What are characterization tests?

Using the Python interactive shell to understand the code

Writing a characterization test

Using pdb to understand the code

Some common pdb commands

Walking through a pdb session

Techniques to break dependencies

The Rope refactoring library

Separate initialization from execution

Use default values for parameters

Extract the method and test

Inject dependencies

Inherit and test

Stubbing local methods

Extract the method and stub

The cycle continues

Time to refactor

Long-term refactoring

Summary

6. Maintaining Your Test Suite

Goals of test maintenance

Organizing tests

Filesystem layout

Naming conventions

Test suite grouping

Making tests readable

Using docstrings

Using fixtures

Fixtures and patching

Using a custom test case class hierarchy

Writing tests closer to the domain

Writing helper methods

Writing better asserts

Using custom equality checkers

Using matchers

Summary

7. Executable Documentation with doctest

Our first doctest

Running the doctest

Test failures

Testing for exceptions

Package-level doctests

Maintaining doctests

Running a suite of doctests

Setup and teardown

Limitations of doctest

Doctest directives

How do doctests fit into the TDD process?

Summary

8. Extending unittest with nose2

Getting started with nose2

Writing tests for nose2

Setup and teardown

Parameterized tests

Generated tests

Layers

nose2 plugins

Doctest support

Writing test results to an XML file

Measuring test coverage

Debugging test failures

nose2 configuration

Summary

9. Unit Testing Patterns

Pattern – fast tests

Pattern – running a subset of tests

Test loaders

Using the load_tests protocol

Skipping tests

Pattern – using attributes

Attributes with vanilla unittests

Pattern – expected failures

Pattern – data-driven tests

Pattern – integration and system tests

Pattern – spies

Pattern – asserting a sequence of calls

Pattern – patching the open function

Pattern – mocking with mutable args

Summary

10. Tools to Improve Test-Driven Development

TDD tools

py.test

py.test versus nose2

Trial

Sure

PyHamcrest

Integrating with build tools

Paver

Integrating with packaging tools

Setuptools

Distutils

Integrating with continuous integration tools

Jenkins

Travis CI

Other tools

tox

Sphinx

IDE integration

Summary

A. Answers to Exercises

Red-Green-Refactor – The TDD Cycle

Code Smells and Refactoring

B. Working with Older Python Versions

Writing code that is compatible across versions

Running tests from the command line

Running the examples in this book

Index

Test-Driven Python Development

Copyright © 2015 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: April 2015

Production reference: 1210415

Published by Packt Publishing Ltd.

Livery Place

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Birmingham B3 2PB, UK.

ISBN 978-1-78398-792-4

www.packtpub.com

Cover image by Jayanand Govindaraj (<[email protected]>)

Credits

Author

Siddharta Govindaraj

Reviewers

Sharad Bagri

Kevin Davenport

Vivek Vidyasagaran

Devesh Chanchlani

Dorai Thodla

Kiran Gangadharan

Cees de Groot

David Simick

Fernando Ramos

Christopher Humphries

Commissioning Editor

Julian Ursell

Acquisition Editor

Nikhil Karkal

Content Development Editor

Sumeet Sawant

Technical Editor

Ruchi Desai

Copy Editors

Vikrant Phadke

Sameen Siddiqui

Alpha Singh

Project Coordinator

Danuta Jones

Proofreaders

Simran Bhogal

Stephen Copestake

Safis Editing

Paul Hindle

Indexer

Mariammal Chettiyar

Graphics

Jason Monteiro

Production Coordinator

Arvindkumar Gupta

Cover Work

Arvindkumar Gupta

About the Author

Siddharta Govindaraj first encountered Python in 2002, and it has remained his favorite programming language ever since. He was an early participant in BangPypers, India's first Python community, and a speaker at InPycon. He is the founder of Silver Stripe Software, an Indian product start-up that develops products based on Python. A vocal proponent of the language, Siddharta extols the virtues of Python to anyone who will listen—and also to those who won't. His blog is at http://www.siddharta.me.

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