Ensures single click event invocation

Adds a wait to ensure that the click event is only invoked a single time after a click.

Author: Keboo

tests/MaterialDesignThemes.UITests/WPF/SplitButtons/SplitButtonTests.cs

@@ -99,12 +99,14 @@ public async Task SplitButton_WithButtonInPopup_CanBeInvoked()
         await Wait.For(async () => await popupContent.GetIsVisible());
         await Wait.For(async () => await popupContent.GetActualHeight() > 10);
         await popupContent.LeftClick();
-        await Task.Delay(50);
 
         // Assert
-        var invocations = await clickEvent.GetInvocations();
-        Assert.Single(invocations);
-
+        await Wait.For(async () =>
+        {
+            var invocations = await clickEvent.GetInvocations();
+            Assert.Single(invocations);
+        });
+        
         recorder.Success();
     }