[net7.0] Fix reliability of RemoveLastPage test (#13679)

Backport of #13663 to net7.0

/cc @rmarinho @PureWeen

src/Controls/tests/Core.UnitTests/NavigationPageLifecycleTests.cs

@@ -91,30 +91,23 @@ public async Task PopLifeCycle(bool useMaui)
 		[InlineData(true)]
 		public async Task RemoveLastPage(bool useMaui)
 		{
-			ContentPage initialPage = new ContentPage();
-			ContentPage pushedPage = new ContentPage();
+			var initialPage = new PageLifeCycleTests.LCPage();
+			var pushedPage = new PageLifeCycleTests.LCPage();
 
-			ContentPage initialPageAppearing = null;
-			ContentPage pageDisappeared = null;
-
-			NavigationPage nav = new TestNavigationPage(useMaui, initialPage);
+			var nav = new TestNavigationPage(useMaui, initialPage);
 			_ = new TestWindow(nav);
-			nav.SendAppearing();
-
-			initialPage.Appearing += (sender, _)
-				=> initialPageAppearing = (ContentPage)sender;
-
-			pushedPage.Disappearing += (sender, _)
-				=> pageDisappeared = (ContentPage)sender;
 
 			await nav.PushAsync(pushedPage);
-			Assert.Null(initialPageAppearing);
-			Assert.Null(pageDisappeared);
+			Assert.Equal(1, initialPage.AppearingCount);
+			Assert.Equal(1, pushedPage.AppearingCount);
+			Assert.Equal(0, pushedPage.DisappearingCount);
 
 			nav.Navigation.RemovePage(pushedPage);
+			await nav.NavigatingTask;
 
-			Assert.Equal(initialPageAppearing, initialPage);
-			Assert.Equal(pageDisappeared, pushedPage);
+			Assert.Equal(2, initialPage.AppearingCount);
+			Assert.Equal(1, pushedPage.AppearingCount);
+			Assert.Equal(1, pushedPage.DisappearingCount);
 		}
 
 		[Theory]

src/Controls/tests/Core.UnitTests/PageLifeCycleTests.cs

@@ -211,7 +211,7 @@ public async Task PushSecondModalPage()
 			Assert.Equal(1, firstModalPage.AppearingCount);
 		}
 
-		class LCPage : ContentPage
+		public class LCPage : ContentPage
 		{
 			public NavigatedFromEventArgs NavigatedFromArgs { get; private set; }
 			public NavigatingFromEventArgs NavigatingFromArgs { get; private set; }

src/Controls/tests/Core.UnitTests/TestClasses/TestNavigationPage.cs

@@ -39,7 +39,7 @@ public async Task<bool> SendBackButtonPressedAsync()
 			return result;
 		}
 
-
+		public Task NavigatingTask => Handler?.NavigatingTask ?? Task.CompletedTask;
 	}
 
 	public class TestNavigationHandler : ViewHandler<NavigationPage, object>
@@ -54,24 +54,36 @@ public static PropertyMapper<IStackNavigationView, TestNavigationHandler> Naviga
 
 		public NavigationRequest CurrentNavigationRequest { get; private set; }
 
+		TaskCompletionSource _navigationSource;
+
+		public Task NavigatingTask => (_navigationSource?.Task ?? Task.CompletedTask);
 
-		public void CompleteCurrentNavigation()
+		public async void CompleteCurrentNavigation()
 		{
 			if (CurrentNavigationRequest == null)
 				throw new InvalidOperationException("No Active Navigation in the works");
 
 			var newStack = CurrentNavigationRequest.NavigationStack.ToList();
 			CurrentNavigationRequest = null;
 
+			var source = _navigationSource;
+			_navigationSource = null;
+
 			if ((this as IElementHandler).VirtualView is IStackNavigation sn)
 				sn.NavigationFinished(newStack);
+
+
+			await Task.Delay(1);
+			source.SetResult();
 		}
 
 		async void RequestNavigation(NavigationRequest navigationRequest)
 		{
-			if (CurrentNavigationRequest != null)
+			if (CurrentNavigationRequest != null || _navigationSource != null)
 				throw new InvalidOperationException("Already Processing Navigation");
 
+
+			_navigationSource = new TaskCompletionSource();
 			CurrentNavigationRequest = navigationRequest;
 
 			await Task.Delay(10);