The Case of the Crimson Test Suite

An Introduction to Swift Testing

by Daniel H Steinberg

Check out this quick, hands-on introduction to the new Swift Testing Framework. You’ll learn how easy it is to now write and run tests for your Swift code, and the results are so much cleaner and clearer. You’ll collect some tests in a suite and use tags to group others. You’ll write expectations and requirements and learn various techniques to combine and simplify them. You’ll actually look forward to testing your code.

This work was written and produced entirely by the author. We are proud to be distributing it.

The Case of the Crimson Test Suite is an introduction to the modern Swift Testing framework.

Testing your packages and apps for Apple platforms has never been easier. The new Swift Testing framework makes it easy for you to write tests that are clean and clear with easy-to-read feedback when a test fails. In this book we begin with tests that run as freestanding functions. Later, we gather some of them up into a suite so that we can run a test individually, as part of a suite, or as one of the entire tests in the current test plan.

You’ll write expectations and requirements to test the result of calling your production code, and you’ll verify methods that should and do throw an error. You’ll test asynchronous code and, in those rare cases when it’s needed, write serialized tests. By default Swift Testing runs your tests in parallel in random order for both improved performance and to catch hidden dependencies. You’ll create display names and use test description to improve the test output and introduce tags so that you can run a subset of your tests without suites or across many suites.

You need a Mac running Xcode 16.

Source code

Errata

Releases:

• P1.0 2024/12/03

Chapter 1: Getting Started excerpt

• The Agile Detective
• A Project with Tests
• Adding a Test Target to a Project
• A Package with Tests
• Adding a Test Target to a Package
• Road Map
• Credits

Chapter 2: The Basics of Swift Testing excerpt

• A Clean Slate
• Testing an init()
• Testing a Computed Property
• Multiple Expectations
• Display Names
• Tags
• Testing the Public Interface
• Observable

Chapter 3: Test Organization and Flow

• The Calculator Project
• Test Driving the Stack
• Testing Errors
• #expect(throws:)
• #require()
• Group the Tests
• Suite
• Suite in a Suite

Chapter 4: The Finer Points excerpt

• Serial and Parallel
• More Serial Tests
• Cross-Contamination
• Testing Async Code
• Unary Operators
• Binary Operators
• Parametrized Tests
• More Parametrized Tests
• Test Description

Daniel H Steinberg is the author of more than a dozen books including the best selling books A Functional Programming Kickstart, A Swift Kickstart, Second Edition and Dear Elena. He has written apps for the iPhone and the iPad since the SDKs first appeared and has written programs for the Mac all the way back to System 7.

Daniel presents iOS, Functional Programming, SwiftUI, and Swift training and consults through his company Dim Sum Thinking. When he’s not coding or talking about coding for the Mac, the iPhone, and the iPad he’s probably cooking, baking bread, or hanging out with friends. Details on his training and speaking are on the Dim Sum Thinking website.