Chapters
Chapters

Chapters

Hide chapters

RxSwift: Reactive Programming with Swift

Fourth Edition · iOS 13 · Swift 5.1 · Xcode 11

Before You Begin

Section 0: 4 chapters
Show chapters Hide chapters

Section I: Getting Started with RxSwift

Section 1: 4 chapters
Show chapters Hide chapters

Section II: Operators & Best Practices

Section 2: 7 chapters
Show chapters Hide chapters

Section III: iOS Apps with RxCocoa

Section 3: 2 chapters
Show chapters Hide chapters

Section IV: Intermediate RxSwift/RxCocoa

Section 4: 4 chapters
Show chapters Hide chapters

Section V: RxSwift Community Cookbook

Section 5: 6 chapters
Show chapters Hide chapters

Section VI: Putting It All Together

Section 6: 3 chapters
Show chapters Hide chapters

16. Testing with RxTest
Written by Scott Gardner

Heads up... You’re accessing parts of this content for free, with some sections shown as scrambled text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

Heads up... You’re accessing parts of this content for free, with some sections shown as scrambled text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

👏🏼 💯🚀

☝🏼 That’s for you, for not skipping this chapter. Studies show that there are two reasons why developers skip writing tests:

  1. They write bug-free code.
  2. Writing tests isn’t fun.

If the first reason is all you, you’re hired! And if you agree with the second reason, well, let me introduce you to my little friend: RxTest.

For all the reasons why you started reading this book and are excited to begin using RxSwift in your app projects, RxTest and RxBlocking should get you excited to write tests against your RxSwift code, too. They provide an elegant API that makes writing tests easy and fun.

This chapter will introduce you to RxTest and RxBlocking. You’ll write tests against several RxSwift operators and production RxSwift code in an iOS app project.

Getting started

The starter project for this chapter is named Testing, and it contains a handy app to give you the red, green, and blue values and color name if available for the hex color code you enter. After running pod install, open up the project workspace and run it. You will see the app starts off with rayWenderlichGreen, but you can enter any hex color code and get the RGB and name values.

This app is organized using the MVVM design pattern, which you’ll learn about in Chapter 24, “MVVM with RxSwift.” The view model contains the following logic that the view controller will use to control the view, and you’ll write tests against this logic later in the chapter:

// Convert hex text to color
color = hexString
  .map { hex in
    guard hex.count == 7 else { return .clear }
    let color = UIColor(hex: hex)
    return color
  }
  .asDriver(onErrorJustReturn: .clear)

// Convert the color to an rgb tuple
rgb = color
  .map { color in
    var red: CGFloat = 0.0
    var green: CGFloat = 0.0
    var blue: CGFloat = 0.0

    color.getRed(&red, green: &green, blue: &blue, alpha: nil)
    let rgb = (Int(red * 255.0), Int(green * 255.0), Int(blue * 255.0))
    return rgb
  }
  .asDriver(onErrorJustReturn: (0, 0, 0))

// Convert the hex text to a matching name
colorName = hexString
  .map { hexString in
    let hex = String(hexString.dropFirst())

    if let color = ColorName(rawValue: hex) {
      return "\(color)"
    } else {
      return "--"
    }
  }
  .asDriver(onErrorJustReturn: "")

Before diving into testing this code, you’ll learn about RxTest by writing a few tests against RxSwift operators.

Note: This chapter presumes you are familiar with writing unit tests in iOS using XCTest. If you’re new to unit testing in iOS, check out our video course, Beginning iOS Unit and UI Testing at https://videos.raywenderlich.com/courses/57-beginning-ios-unit-and-ui-testing/lessons/1.

Testing operators with RxTest

RxTest is a separate library from RxSwift. It’s hosted within the RxSwift repo but requires a separate pod install and import. RxTest provides many useful additions for testing RxSwift code, including:

What are hot and cold observables?

RxSwift goes to great lengths to streamline and simplify your Rx code. There are circles of thought in the RxSwift community that feel hot and cold should be thought of as traits of observables instead of concrete types.

Using RxBlocking

RxBlocking is another library housed within the RxSwift repo that has its own pod and must be separately imported. Its primary purpose is to convert an observable to a BlockingObservable via its toBlocking(timeout:) method. What this does is block the current thread until the observable terminates, either normally or by reaching the timeout. The timeout argument is an optional TimeInterval which is nil by default. If you set a value for timeout and that time interval elapses before the observable terminates normally, toBlocking will throw an RxError.timeout error. This essentially turns an asynchronous operation into a synchronous one, which makes testing much easier.

Testing RxSwift production code

Start by opening ViewModel.swift in the Testing group. At the top, you’ll see these property definitions:

Where to go from here?

Writing tests using RxText and RxBlocking is similar to writing data and UI binding code using RxSwift and RxCocoa. There are no challenges for this chapter, because you will be doing more view model testing in Chapter 24, “MVVM with RxSwift.” Happy testing!

15. Intro to Schedulers
17. Creating Custom Reactive Extensions
Have a technical question? Want to report a bug? You can ask questions and report bugs to the book authors in our official book forum here.
© 2026 Kodeco Inc.

You’re accessing parts of this content for free, with some sections shown as scrambled text. Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now