Fix LocationChangingHandlers_CannotCancelTheNavigationAsynchronously_UntilReturning (#54388)

Author: MackinnonBuck

src/Components/Components/test/NavigationManagerTest.cs

@@ -805,6 +805,7 @@ public async Task LocationChangingHandlers_CannotCancelTheNavigationAsynchronous
         // Arrange
         var baseUri = "scheme://host/";
         var navigationManager = new TestNavigationManager(baseUri);
+        var blockPreventNavigationTcs = new TaskCompletionSource();
         var navigationPreventedTcs = new TaskCompletionSource();
         var completeHandlerTcs = new TaskCompletionSource();
         LocationChangingContext currentContext = null;
@@ -814,10 +815,14 @@ public async Task LocationChangingHandlers_CannotCancelTheNavigationAsynchronous
         // Act/Assert
         var navigation1 = navigationManager.RunNotifyLocationChangingAsync($"{baseUri}/subdir1", null, false);
 
+        // Unblock the location changing handler to let it cancel the navigation, now that we know the
+        // navigation wasn't canceled synchronously
+        blockPreventNavigationTcs.SetResult();
+
         // Wait for the navigation to be prevented asynchronously
         await navigationPreventedTcs.Task.WaitAsync(Timeout);
 
-        // Assert that we have prevented the navigation but the cancellation token has requested cancellation
+        // Assert that we have prevented the navigation but the cancellation token has not requested cancellation
         Assert.True(currentContext.DidPreventNavigation);
         Assert.False(currentContext.CancellationToken.IsCancellationRequested);
 
@@ -835,7 +840,7 @@ async ValueTask HandleLocationChanging(LocationChangingContext context)
             currentContext = context;
 
             // Force the navigation to be prevented asynchronously
-            await Task.Yield();
+            await blockPreventNavigationTcs.Task;
 
             context.PreventNavigation();
             navigationPreventedTcs.SetResult();