Unit Test SwiftUI redraws demo from OpenSwiftUI code

DemoTests.swift

import Testing
import SwiftUI
@testable import Demo

typealias PlatformViewController = UIViewController
typealias PlatformWindow = UIWindow
typealias PlatformHostingController = UIHostingController

extension PlatformViewController {
    // NOTE: Remember to withExtendedLifetime for window to ensure it is not deallocated duration animation or update.
    func triggerLayout() {
        #if os(iOS)
        let window = UIWindow(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
        window.rootViewController = self
        window.makeKeyAndVisible()
        view.layoutIfNeeded()
        #else
        let window = NSWindow(
            contentRect: CGRect(x: 0, y: 0, width: 100, height: 100),
            styleMask: [.titled, .closable, .resizable],
            backing: .buffered,
            defer: false
        )
        window.contentViewController = self
        window.makeKeyAndOrderFront(nil)
        view.layoutSubtreeIfNeeded()
        #endif
    }
}

@MainActor
func triggerLayoutWithWindow(
    expectedCount: Int = 1,
    _ body: @escaping @MainActor (Confirmation, UnsafeContinuation<Void, Never>) -> PlatformViewController
) async throws {
    var window: PlatformWindow!
    await confirmation(expectedCount: expectedCount) { @MainActor confirmation in
        await withUnsafeContinuation { (continuation: UnsafeContinuation<Void, Never>) in
            let vc = body(confirmation, continuation)
            vc.triggerLayout()
            window = vc.view.window
        }
    }
    #if os(macOS)
    window.isReleasedWhenClosed = false
    window.close()
    #endif
    withExtendedLifetime(window) {}
}


struct DemoTests {
    class Model: ObservableObject {
        @Published var name = ""
        @Published var count = 0
    }

    struct ContentView: View {
        @StateObject private var m = Model()

        var confirmation: Confirmation
        var continuation: UnsafeContinuation<Void, Never>

        var body: some View {
            let _ = confirmation()
            VStack {
                Text(m.name)
                Text(m.count.description)
            }
            .onAppear {
                DispatchQueue.main.async {
                    m.name = "A"
                    DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
                        m.count = 1
                        DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
                            continuation.resume()
                        }
                    }
                }
            }
        }
    }

    @Test
    func observeCount() async throws {
        try await triggerLayoutWithWindow(expectedCount: 3) { confirmation, continuation in
            PlatformHostingController(
                rootView: ContentView(
                    confirmation: confirmation,
                    continuation: continuation
                )
            )
        }
    }
}