Book Image

Test-Driven Python Development

By : Siddharta Govindaraj
Book Image

Test-Driven Python Development

By: Siddharta Govindaraj

Overview of this book

This book starts with a look at the test-driven development process, and how it is different from the traditional way of writing code. All the concepts are presented in the context of a real application that is developed in a step-by-step manner over the course of the book. While exploring the common types of smelly code, we will go back into our example project and clean up the smells that we find. Additionally, we will use mocking to implement the parts of our example project that depend on other systems. Towards the end of the book, we'll take a look at the most common patterns and anti-patterns associated with test-driven development, including integration of test results into the development process.
Table of Contents (20 chapters)
Test-Driven Python Development
About the Author
About the Reviewers

Limitations of doctest

The biggest limitation of doctest is that it only compares printed output. This means that any output that could be variable will lead to test failures. The following is an example:

>>> exchange
{'GOOG': <stock_alerter.stock.Stock object at 0x00000000031F8550>, 'AAPL': <stock_alerter.stock.Stock object at 0x00000000031F8588>}

This doctest has the potential to fail for two reasons:

  • The order in which a dictionary object is printed out is not guaranteed by Python, which means it could be printed out in the opposite order, sometimes leading to failure

  • The Stock object might be at a different address each time, so that part will fail to match the next time the test is run

The solution to the first problem is to ensure that the output is deterministic. For example, the following approach will work:

>>> for key in sorted(exchange.keys()):
...    print(key, exchange[key])
AAPL <stock_alerter.stock.Stock object at 0x00000000031F8550>