So what’s in all of these new chapters?

• More on parametrization, markers, coverage, mocking, tox and continuous integration, and third-party plugins. All of these topics were covered in the first edition, but in this edition I expand that coverage. I pulled the discussion of parametrization into its own chapter and added a discussion of advanced parametrization techniques. I delve more deeply into markers and include an example of how to pass data from markers to fixtures (which is super cool). I also take you on a deeper dive into test coverage, mocking, and CI, and using and building your own plugins to extend pytest’s capabilities.
• A discussion of test strategy. Feedback from the first edition was that the book was great for the mechanics of how to use pytest, but the “What test do I write?” information was a bit lacking. The new Chapter 7, ​Strategy​ is a push in the right direction of what tests to write. A complete treatment of test strategy would be a book in itself; however, this chapter will get you started.
• Information about the Python search path. A lot of readers reached out to me asking about how to get their tests to see their test code, and the first edition didn’t cover it. The project in this book, Cards, doesn’t have that problem because it’s an installed Python package. However, lots of user projects are applications or scripts or lots of other things that are not installed packages. This chapter offers a focused look at the problem and provides some solutions.

I consolidated the information about debugging test failures into a chapter of its own. In the last edition, this information was spread all throughout the book. It is my hope that when you are faced with a deadline and a failing test suite, bringing this information together into one chapter will help you figure out an answer quickly and ease some stress.

Finally, the example project changed. The first edition used a project called Tasks to illustrate how to use pytest. Now it’s called Cards. Here’s why:

• It’s easier to say out loud. (Try it. Say “tasks” three times, then “cards” three times. Right?)
• The new project itself is different because it uses Typer instead of Click for command-line functionality. Typer code is easier to read.
• The project also uses Rich for formatting the output. Rich didn’t exist (neither did Typer) when the first edition was written.

The code examples have also been simplified. The directory structure of the first edition code examples followed a progression of a possible test directory within a project, with most of the project removed. Seriously, I think it made sense to me at the time. In this edition, there is a project in its own directory, cards_proj, with no tests. Then, each of the chapters have test code (if appropriate) that either work on the one project or on some local code. Trust me, I think you’ll agree that it’s way easier to follow along now.