Python Testing: Beginner's Guide

255 Pages·2010·2.54 MB·English

by  Arbuckle, Daniel

Python Testing
Beginner's Guide
An easy and convenient approach to testing your
Python projects
Daniel Arbuckle

BIRMINGHAM - MUMBAI
This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
Python Testing
Beginner's Guide
Copyright © 2010 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
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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: January 2010
Production Reference: 1120110
Published by Packt Publishing Ltd.
32 Lincoln Road
Olton
Birmingham, B27 6PA, UK.
ISBN 978-1-847198-84-6
www.packtpub.com
Cover Image by Vinayak Chittar ([email protected])
This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
Credits
Author Production Editorial Manager
Daniel Arbuckle Abhijeet Deobhakta
Reviewers Editorial Team Leader
Róman Joost Aanchal Kumar
Andrew Nicholson
Project Team Leader
Herjend Teny
Lata Basantani
Acquisition Editor
Project Coordinator
Douglas Paterson
Srimoyee Ghoshal
Development Editor
Graphics
Ved Prakash Jha
Geetanjali Sawant
Technical Editors
Production Coordinator
Aditya Belpathak
Shantanu Zagade
Charumathi Sankaran
Cover Work
Indexer
Shantanu Zagade
Monica Ajmera Mehta
Proofreader
Lesley Harrison
This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
About the Author
Daniel Arbuckle received his Ph. D. in computer science from the University of Southern
California in 2007. He is an active member of the Python community and an avid unit tester.
I would like to thank Grig, Titus, and my family for their companionship and
encouragement along the way.
About the Reviewers
Róman Joost is a professional Python software developer and a free software enthusiast,
currently living in Australia. Since 2003, he has been contributing to the GNU Image
Manipulation Program (GIMP) by writing documentation and contributing to the source
code. He uses testing frameworks and test-driven methodologies extensively, when writing
new components for the Z Object Publishing Environment (Zope) in Python.
Andrew Nicholson is a software engineer with over 12 years of professional commercial
experience in a broad range of technologies. He is passionate about free and open source
software (FOSS) and has actively participated in contributing code, ideas, and passion in the
open source community since 1999.
Nicholson's biography can be read at http://infiniterecursion.com.au/people/.
Herjend Teny is an electrical engineering graduate from Melbourne who has come to love
programming in Python after years of programming in mainline programming languages,
such as C, Java, and Pascal.
He is currently involved in designing web application using Django for an Article Repository
project on http://www.havingfunwithlinux.com/. The project would allow users to
post their article for public view and bookmark it onto their favorite blog.
This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
Table of Contents
Preface 1
Chapter 1: Testing for Fun and Profit 7
How can testing help? 8
Types of testing 9
Unit testing 9
Integration testing 9
System testing 9
You've got Python, right? 10
Summary 10
Chapter 2: Doctest: The Easiest Testing Tool 11
Basic doctest 11
Time for action – creating and running your first doctest 12
The syntax of doctests 13
Time for action – writing a more complex test 14
Expecting exceptions 15
Time for action – expecting an exception 16
Expecting blank lines in the output 17
Using directives to control doctest 17
Ignoring part of the result 17
Time for action – using ellipsis in tests 17
Ignoring whitespace 18
Time for action – normalizing whitespace 19
Skipping an example entirely 19
Time for action – skipping tests 20
Other doctest directives 21
Execution scope 21
Embedding doctests in Python docstrings 24
Time for action – embedding a doctest in a docstring 24
Doctest directives 25
Table of Contents
Execution scope 26
Putting it in practice: an AVL tree 26
English specification 27
Node data 28
Constructor 30
Recalculate height 30
Make deletable 32
Rotation 33
Locating a node 34
Testing the rest of the specification 34
Summary 35
Chapter 3: Unit Testing with Doctest 37
What is Unit testing and what it is not? 37
Time for action – identifying units 38
Unit testing throughout the development process 40
Design phase 41
Time for action – unit testing during design 41
Development phase 44
Time for action – unit testing during development 44
Feedback phase 47
Time for action – unit testing during feedback 47
Back to the development phase 51
Time for action – unit testing during development... again 51
Maintenance phase 53
Time for action – unit testing during maintenance 53
Reuse phase 55
Time for action – unit testing during reuse 55
Summary 59
Chapter 4: Breaking Tight Coupling by using Mock Objects 61
Installing Python Mocker 61
Time for action – installing Python Mocker 62
The idea of a mock object 62
Python Mocker 63
Time for action – exploring the basics of Mocker 63
Mocking functions 67
Mocking containers 68
Parameter matching 69
ANY 69
ARGS 70
KWARGS 70
IS 71
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This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
Table of Contents
IN 71
CONTAINS 72
MATCH 72
Mocking complex expressions 73
Returning iterators 73
Raising exceptions 74
Calling functions via a mock 74
Specifying that an expectation should occur multiple times 75
Replacing library objects with mocks 77
Mocking self 80
Time for action – passing a mock object as self 80
Summary 82
Chapter 5: When Doctest isn't Enough: Unittest to the Rescue 83
Basic unittest 83
Time for action – testing PID with unittest 84
Assertions 89
assertTrue 89
assertFalse 90
assertEqual 90
assertNotEqual 90
assertAlmostEqual 90
assertNotAlmostEqual 92
assertRaises 92
fail 93
Test fixtures 94
Time for action – testing database-backed units 95
Integrating with Python Mocker 100
Summary 100
Chapter 6: Running Your Tests: Follow Your Nose 101
What is Nose? 101
Installing Nose 102
Organizing tests 103
Time for action – organizing tests from previous chapters 104
Finding doctests 108
Customizing Nose's search 109
Nose and doctest 110
Time for action – creating a fixture for a doctest 111
Nose and unittest 112
Time for action – creating a module fixture 113
Time for action – creating a package fixture 114
Nose's own testing framework 116
[ iii ]
This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
This material is copyright and is licensed for the sole use by Betty Vaughan-Pope on 1st February 2010
2601 S Broadway St, Unit 29, La Porte, , 77571
Table of Contents
Time for action – using Nose-specific tests 116
Summary 118
Chapter 7: Developing a Test-Driven Project 119
Writing the specification 119
Time for action – what are you going to do? 125
Writing initial unit tests 125
Time for action – nailing down the specification with unit tests 139
Coding planner.data 139
Using the tests to get the code right 143
Fixing the code 143
Time for action – writing and debugging code 146
Writing persistence tests 147
Writing persistence code 148
Finishing up 151
Summary 153
Chapter 8: Testing Web Application Frontends using Twill 155
Installing Twill 155
Exploring the Twill language 156
Time for action – browsing the web with Twill 156
Time for action – Twill scripting 159
Twill commands 160
help 160
setglobal 160
setlocal 161
add_auth 161
add_extra_header 161
clear_extra_headers 162
show_extra_headers 162
agent 162
back 162
clear_cookies 162
code 162
config 163
debug 163
echo 163
exit 163
extend_with 164
find 164
notfind 164
follow 164
formaction 164
formclear 165
formfile 165
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