Writing software is hard. Even the smallest projects have many moving parts. We developers are not only expected to get those parts moving, but keep them moving as the application changes over time. Test-Driven Development (TDD) is a methodology that allows us to quantify the successful function of each of these parts before we attempt to code them. Using TDD, we can focus on a single part of the application at a time, leaving a trail of tests that guard against regression as we continue to update the application.
Django is a popular web framework written in Python. Its batteries-included: the framework itself includes URL routing, object-relational mapping, templates, and many other necessities for building a modern web application. This book will take you through the process of developing a Django app by writing failing tests first, then writing application code to make those tests pass.
Chapter 1, Keeping Your Promises, describes the benefits of TDD in comparison to other styles of programming. We'll look at a very simple example, and talk about testing as a pillar of professional software development.
Chapter 2, Your First Test-Driven Application, introduces the example application that we'll be building throughout the book. We'll translate a user story into a browser-based functional test using Selenium, and write unit tests and application code to start to fulfill that user story.
Chapter 3, Ironclad Code, continues where the previous chapter left off, digging deeper into the API available for writing unit tests in Django. We'll cover the Python Debugger and tools for simulating web requests.
Chapter 4, Building Out and Refactoring, adds new features to the application. We'll use our test suite to maintain existing functionality while refactoring to keep our code tidy and maintainable.
Chapter 5, User Stories As Code, focuses on writing functional tests and the packages available to drive the browser during a test run. We'll learn how to select and click on elements, submit forms, switch between open windows, and perform other user actions in our UI.
Chapter 6, No App Is an Island, applies the TDD methodology to third-party API integration. We'll learn when, why, and how to mock out HTTP requests inside a single unit test so that our tests aren't relying on an outside resource (even if our app is).
Chapter 7, Share and Share Alike, introduces Django REST Framework—a tool for building a REST API with Django. We'll cover the importance of documentation when writing an API, and use the framework's tools to send requests to the API during tests.
Chapter 8, Promises Kept, takes a look back at what we've learned, and whether we've realized all the benefits from the first chapter. We'll get suggestions for next steps in TDD, and talk about some of the common pitfalls you may encounter.
In order to follow along with the examples in this book, you'll need a computer with a command line interface (the default is Terminal for Linux and Mac, and Command Prompt for Windows) with Python installed. You will also need an Internet connection to download third-party packages and a text editor for writing Python code.
This book is for Django developers who want to learn about TDD, and how it might help them in their work. It's expected that the reader is comfortable with reading and writing Python and has some familiarity with the Django framework.
In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.
Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "If you're making HTTP calls, the requests package is a great option."
A block of code is set as follows:
# multiplicator.py
defmultiplicator(x, y):
passAny command-line input or output is written as follows:
$ python >>> from multiplicator import multiplicator >>>multiplicator(2, 3) 6
New terms and important words are shown in bold, like this: " A Continuous Integration (CI) server, for our purposes, can pull our project from version control "
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The source code for the sample application is available on GitHub at https://github.com/kevinharvey/jmad on the test-driven-django-development branch (the repository's default). Development milestones in the book have been tagged with names like ch5-2-staff-login to make navigating the repository easier.
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