This book is for intermediate iOS developers who already know the basics of iOS and Swift development but want to learn how to write code which is both testable and maintainable.
To start, you’ll learn the TDD Cycle and how to implement these concepts within an iOS application. The book then takes you through Test Expressions and Expectation so that you can test synchronous code. You’ll then write tests to verify networking endpoints and the ability to mock the returned results, followed by writing tests that run against authentication endpoints. Continue trouble-shooting your apps by understanding common legacy problems, as well as breaking dependencies into modules. And, finally, refactor large classes into smaller, more manageable classes and objects.
Before You Begin
This section tells you a few things you need to know before you get started, such as what you’ll need for hardware and software, where to find the project files for this book, and more.
This section is a high-level introduction to test-driven development, how it works and why you should use it. You’ll also learn about the TDD cycle in this chapter, and you’ll use this throughout the rest of the book.
This chapter covers how to use the XCTAssert functions.
These are the primary actors of the test infrastructure.
Next, you'll learn how to use the host application to drive view unit testing.
Then, you'll go through gathering code coverage to verify the minimum amount of testing.
Finally, you'll use the test debugger to find and fix test errors.
In the previous chapters you built out the app's state based upon what the user can do with the Start button. The main part of the app relies on responding to changes as the user moves around and records steps. These actions create events outside the program's control.
XCTestExpectation is the tool for testing things that happen outside the direct flow.
In this chapter you'll learn how to use mocks to test code that depends on system or external services without needing to call services: They may not be available, usable or reliable.
These techniques allow you to test error conditions like a failed save and to isolate logic from SDKs like CoreMotion and HealthKit.
Section III: TDD With Networking
This section will teach you test-driven development with networking.
You’ll get hands-on experience creating a puppy-buying app that interacts with a backend service. You’ll learn how to do TDD for RESTful networking, using network clients and downloading images throughout this section.
You'll complete a puppy-adoption app called Dog Patch throughout this section.
This app connects dog lovers with kind, professional breeders to find the puppy of their dreams.
A prospective owner first browses available puppy listings within the app.
You'll use TDD to create an ImageClient for handling images. You can use ImageClient anywhere you need it in the app.
Section IV: TDD in Legacy Apps
This section will show you how to start test-driven development in a legacy app that lacks sufficient unit tests. You’ll learn strategies for introducing TDD into existing apps, methods for visualizing and splitting up dependencies, ways to add features safely alongside existing code and how to refactor large classes.
Throughout this section, you’ll introduce TDD into an app for managing a business. The app is feature-rich with spaghetti code and ready for a TDD clean up!
Several techniques and concepts in this section were inspired by Michael Feather’s book Working Effectively with Legacy Code. Reading that book isn’t a strict requirement for working through these chapters. However, you’ll likely benefit by having some familiarity with the topics herein if you already have read it!
Beginning TDD on an existing, “legacy” project is much different than starting TDD on a new project. Often times, the original team has long left, and the code base is not fully understood. The project has few if any unit tests, lacks documentation and is slow to build.
It’s always safer to make a change when you have tests in place already.
In the absence of existing tests, however, you may need to make changes just to be able to add tests! One of the most common reasons for this is tightly-coupled dependencies: you can’t add tests to a class because it depends on other classes that depend on other classes… View controllers especially are often victims to this issue.
You’ll continue the work from the last chapter, further breaking **MyBiz** into modules so you can reuse the login functionality. You’ll learn how to define clean boundaries in the code to create logical units. Through the use of tests, you’ll make sure the new architecture works and the app continues to function.
You won’t always have the time, or it may simply not be feasible, to break dependencies of a very large class. In this chapter, you’ll learn strategies to add functionality to an existing class while at the same time avoiding modifying it! You’ll learn two main strategies to do this: Sprouts and Decorators.