SwiftUI Easter Eggs: Performance Benchmarking with _ViewTest and more

TestsApp.swift

import SwiftUI

@main
struct App {
    static func main() {
        _TestApp().runBenchmarks([Benchmark()])
    }
}

extension UIHostingController: _Test where Content == AnyView {}
extension UIHostingController: _ViewTest where Content == AnyView {
    public func initRootView() -> AnyView {
        return rootView
    }
    public func initSize() -> CGSize {
        sizeThatFits(in: UIScreen.main.bounds.size)
    }
}

struct ToggleView: View {    
    var id: String { "HackeryToggleViewID" }

    var body: some View {
        Toggle()._identified(by: id)
    }
}

struct Toggle: View {
    @State var isOn = true

    var id: String { "HackeryToggleID" }

    var body: some View {
        SwiftUI.Toggle(isOn: $isOn, label: { Text("Hackery not allowed") })._identified(by: id)
    }
}

struct PerformanceTest: _PerformanceTest {
    var name = "Hackery Toggle Test"
    func runTest(host: SwiftUI._BenchmarkHost, options: [Swift.AnyHashable : Any]) {
        let test = _makeUIHostingController(AnyView(toggleView)) as! UIHostingController<AnyView>
        test.setUpTest()
        test.render()
        test._forEachIdentifiedView { proxy in
            let state = test.stateForIdentifier(proxy.identifier, type: Bool.self, in: type(of: test.rootView))
            let view = test.viewForIdentifier(proxy.identifier, Toggle.self)
            print("IDENTIFIER: \(proxy)")
            print("STATE: \(state)")
            print("VIEW: \(view)")
        }
        test.tearDownTest()
    }
    
    @ViewBuilder
    var toggleView: some View {
        ToggleView()
    }
}

struct Benchmark: _Benchmark {
    func measure(host: _BenchmarkHost) -> [Swift.Double] {
        return [
            host.measureAction {
                PerformanceTest().runTest(host: host, options: [:])
            },
//            host.measureAction {
//                PerformanceTest2().runTest(host: host, options: [:])
//            },
//            host.measureAction {
//                PerformanceTest3().runTest(host: host, options: [:])
//            },
        ]
    }
}