Writing testable UI related code with modern Swift

[stephencelis]

@grynspan

As a general rule, polling is not recommended in Swift. Instead, see if you can leverage the features of Swift concurrency to suspend the test until the data you need is available.

This is not always possible, especially when you want to test an async endpoint that is stateful over time, or where you need to wiggle your way in between a method's suspension points, as I believe is the case here, and is a very common case with observable models in SwiftUI.

The three year old thread linked above has an example that I believe is still not possible to reliably test in Swift today:

Reliably testing code that adopts Swift Concurrency?

I’m having a hard time figuring out how to test application code as it adopts async-await and begins to be scheduled concurrently. I’ll try to show a simple example. Here’s a basic SwiftUI application that tracks how many times a user has taken a screen shot. It has a view model with an endpoint that spins off some async work, and then the view calls this endpoint when it first appears: class ViewModel: ObservableObject { @Published var count = 0 @MainActor func task() async { let …