Wednesday, July 27, 2011

Book review: “Python Testing Cookbook” by Greg L. Turnquist

Disclosure: a free e-copy of this book was received from the publisher for review purposes. The opinions expressed here are entirely my own; a copy of this review has also been posted at Amazon.

Greg L. Turnquist’s “Python Testing Cookbook” explores automated testing at all levels, with the intention of providing the reader with the knowledge needed to implement testing using Python tools to improve software quality. To this end the book presents over 70 “recipes” in its nine chapters (ranging from the basics of unit testing, through test suites, user acceptance and web application testing, continuous integration, and methods for smoke- and load-testing), covering both tools for testing Python, and Python tools for testing. It also delivers advice about how to get the most from automated testing, which is as much an art as a science.

The first three chapters introduce the fundamentals: writing, organising and running unit tests, comprehensively covering unittest (Python’s built-in unit testing library), nose (a versatile tool for discovering, running and reporting tests) and doctest (which turns Python docstrings into testable code – a sample of this chapter can be downloaded from Having established a solid foundation, subsequent chapters look at increasingly broader levels of automated testing using the appropriate relevant Python tools: for example, the “lettuce” and “should_DSL” libraries for “behaviour driven development” (an extension of “test driven development” which aims to produce human-readable test cases and reports), and the “Pyccuracy” and “Robot” frameworks for end-user acceptance testing of web applications. Later chapters cover higher level concepts and tools, such as using nose to hook Python tests into “continuous integration” servers (both Jenkins and TeamCity are covered in detail), and assessing test coverage using the “coverage” tool (both as a metric, and to identify areas that need more tests). A detailed chapter on smoke- and load-testing includes practical advice on developing multiple test suites for different scenarios, and methods for stress-testing (for example, by capturing and replaying real world data) to discover weaknesses in a system before going to production. The final chapter distils the author’s experience into general advice on making testing a successful part of your code development methodology, both for new and legacy projects.

There’s a lot of good stuff in this book: the initial chapters on unittest and nose are particularly strong, and I can imagine returning to these in future as a reference. There is also a lot of excellent and hard-won practical advice from the author’s own experience – not only in these early chapters but throughout the book – which is consistently valuable (in this regard the final chapter is a real highlight and could easily stand alone – I will definitely be re-reading it soon). Elsewhere the various tools and topics are presented clearly with plenty of useful detail, and in some cases have demystified things that I’d always assumed were quite esoteric and difficult to do (nose in particular was a revelation to me, but also setting up continuous integration servers and measuring test coverage).

There are a few disappointments: the section on mock objects left me feeling baffled as to how to actually implement them in practice – a shame as it was something that I’d looked forward to learning. I’d also have liked something about approaches for handling difficult testing scenarios such as software which interacts with the file system or with large files – a few hints here would have been invaluable for me. There are typos in some commands and code in a few recipes (e.g. for nose), which meant I had to look up the correct syntax elsewhere – perhaps not so bad, but annoying (especially in a cookbook) – and since the recipes themselves aren’t numbered, this sometimes made it difficult to navigate between them.

However these are fairly minor quibbles, and in conclusion I was impressed with both the breadth of material covered by the book and the level of detail for many topics. Moreover I enjoyed reading it and was often left feeling excited at the prospect of being able to apply the ideas to my own projects, which is I think was one of the author’s aims (and no mean feat for a technical book). I think that the combination of the detail together with the author’s practical advice make this book both an excellent introduction to testing with Python, and a valuable resource to refer back to subsequently.

(Addendum: Greg Turnquist's blog about the book can be found at and features some interesting supplementary material.)

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