add a test displaying a system used as a feedback of another system

Example/SignIn/SignIn.swift

@@ -11,7 +11,7 @@ final class SignInViewModel: ViewModel<SignInViewModel.State, SignInViewModel.Ev
                 SignInViewModel.whenChangingUserName(api: GithubAPI()),
                 SignInViewModel.whenSubmiting(api: GithubAPI())
             ],
-            scheduler: RunLoop.main,
+            scheduler: DispatchQueue.main,
             reducer: SignInViewModel.reduce
         )
     }
@@ -141,6 +141,8 @@ struct SignInView: View {
         self.context = context
     }
 
+    @SwiftUI.State var userName: String = ""
+
     var body: some View {
         return Form {
             Section {
@@ -179,9 +181,21 @@ struct SignInView: View {
                 .textContentType(.newPassword)
             }
             Section {
+                // Seems like a bug in switch view amimation
+                // ¯\_(ツ)_/¯
                 Toggle(isOn: context.binding(for: \.termsAccepted)) {
                     Text("Accept Terms and Conditions")
                 }
+                // When wrapping `UISwitch` into UIViewRepresentable
+                // everything works
+                HStack(
+                    alignment: .center,
+                    spacing: 8
+                ) {
+                    Text("Accept Terms and Conditions")
+                    Spacer()
+                    Switch(isOn: context.binding(for: \.termsAccepted))
+                }
             }
             Section {
                 ZStack {
@@ -264,3 +278,43 @@ extension String {
         return self.addingPercentEncoding(withAllowedCharacters: .urlHostAllowed) ?? ""
     }
 }
+
+struct Switch: UIViewRepresentable {
+    let isOn: Binding<Bool>
+    let animated = true
+
+    func makeUIView(context: UIViewRepresentableContext<Switch>) -> UISwitch {
+        let view = UISwitch(frame: .zero)
+
+        view.addTarget(
+            context.coordinator,
+            action: #selector(Target.action(_:)),
+            for: .valueChanged
+        )
+
+        return view
+    }
+
+    func updateUIView(_ uiView: UISwitch, context: UIViewRepresentableContext<Switch>) {
+        uiView.setOn(isOn.wrappedValue, animated: animated)
+    }
+
+    func makeCoordinator() -> Target {
+        return Target { (view) in
+            self.isOn.wrappedValue = view.isOn
+        }
+    }
+
+    class Target: NSObject {
+        init(action: @escaping (UISwitch) -> Void) {
+            self._action = action
+        }
+
+        private let _action: (UISwitch) -> Void
+
+        @objc
+        func action(_ sender: UISwitch) {
+            _action(sender)
+        }
+    }
+}

Tests/CombineFeedbackTests/CombineFeedbackTests.swift

@@ -128,4 +128,58 @@ class CombineFeedbackTests: XCTestCase {
 
         XCTAssertEqual("initial_a", value)
     }
+
+    func test_system_in_a_system() {
+        let scheduler = TestScheduler()
+
+        let feedback1 = Feedback<String, String>(effects: { state -> AnyPublisher<String, Never> in
+          if state.count % 3 == 1 {
+              return Just("a").eraseToAnyPublisher()
+          } else {
+              return Empty<String,Never>().eraseToAnyPublisher()
+          }
+        })
+
+        let feedback2 = Feedback<String, String>(effects: { state -> AnyPublisher<String, Never> in
+          if state.count % 3 == 0 {
+              return Just("d").eraseToAnyPublisher()
+          } else {
+              return Empty<String,Never>().eraseToAnyPublisher()
+          }
+        })
+
+        let innerSystem = Feedback<String, String>{ (stringPublisher: AnyPublisher<String, Never>) ->  AnyPublisher<String, Never> in
+            return stringPublisher.flatMap { (string) -> AnyPublisher<String, Never> in
+                return Publishers.system(initial: string,
+                                         feedbacks: [feedback1, feedback2],
+                                         scheduler: scheduler) { (state: String, event: String) -> String in
+                                                return state + event
+                }.filter({ (state) -> Bool in
+                    state.count % 2 == 0
+                }).map({ (state) -> String in
+                    return state + "c"
+                }).eraseToAnyPublisher()
+            }.eraseToAnyPublisher()
+        }
+
+        let outerSystem = Publishers.system(
+            initial: "initial",
+            feedbacks: [innerSystem],
+            scheduler: scheduler,
+            reduce: { (state: String, event: String) -> String in
+                return event
+            }
+        )
+
+        var value: String?
+
+        _ = outerSystem.sink(
+            receiveValue: {
+                value = $0
+            }
+        )
+
+        scheduler.advance()
+        XCTAssertEqual("initialacdc", value)
+    }
 }