Learning to Unit Test The Observable Macro

No more Combine! Observable FTW

Photo by Bernd 📷 Dittrich on Unsplash

During WWDC 2023 Apple swift developers had the opportunity to learn about the shiny new Observation Framework.

That means we no longer need to test @Published properties to maintain full test coverage. That’s quite nice isn’t it?

Unit Testing With Combine

I have simple project that takes an endpoint (https://jsonplaceholder.typicode.com/posts) and displays them on the screen. There’s a simple viewModel to move the network call out of the view, and a simple service in order to use dependency injection for URLSession.

It’s 80 lines of code.

import SwiftUI

struct ContentView: View {
    @ObservedObject var viewModel: ViewModel
    var body: some View {
        ScrollView {
            LazyVStack{
                ForEach(viewModel.posts) { post in
                    Text(post.title)
                }
            }
        }
        .onAppear {
            viewModel.getPosts()
        }
        .alert(
            "Login failed.",
            isPresented: Binding(get: { viewModel.error != nil }, set: { _,_ in viewModel.error = nil })
        ) {
            Button("OK") {
                // TODO: retry mechanism
            }
        } message: {…