Added unit test

Microsoft.Toolkit.Uwp.UI/Triggers/ControlSizeTrigger.cs

@@ -34,7 +34,7 @@ public bool CanTrigger
         /// <summary>
         /// Gets or sets the max width at which to trigger.
         /// This value is exclusive, meaning this trigger
-        /// could be active if the value is < MaxWidth.
+        /// could be active if the value is less than MaxWidth.
         /// </summary>
         public double MaxWidth
         {
@@ -74,7 +74,7 @@ public double MinWidth
         /// <summary>
         /// Gets or sets the max height at which to trigger.
         /// This value is exclusive, meaning this trigger
-        /// could be active if the value is < MaxHeight.
+        /// could be active if the value is less than MaxHeight.
         /// </summary>
         public double MaxHeight
         {
@@ -133,6 +133,11 @@ public FrameworkElement TargetElement
             typeof(ControlSizeTrigger),
             new PropertyMetadata(null, OnTargetElementPropertyChanged));
 
+        /// <summary>
+        /// Gets a value indicating whether the trigger is active.
+        /// </summary>
+        public bool IsActive { get; private set; }
+
         private static void OnTargetElementPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
         {
             ((ControlSizeTrigger)d).UpdateTargetElement((FrameworkElement)e.OldValue, (FrameworkElement)e.NewValue);
@@ -168,11 +173,13 @@ private void UpdateTrigger()
                 return;
             }
 
-            SetActive(
-                MinWidth <= TargetElement.ActualWidth &&
-                TargetElement.ActualWidth < MaxWidth &&
-                MinHeight <= TargetElement.ActualHeight &&
-                TargetElement.ActualHeight < MaxHeight);
+            bool activate = MinWidth <= TargetElement.ActualWidth &&
+                            TargetElement.ActualWidth < MaxWidth &&
+                            MinHeight <= TargetElement.ActualHeight &&
+                            TargetElement.ActualHeight < MaxHeight;
+
+            IsActive = activate;
+            SetActive(activate);
         }
     }
 }

UnitTests/UnitTests.UWP/UI/Triggers/Test_ControlSizeTrigger.cs

@@ -0,0 +1,50 @@
+using Microsoft.Toolkit.Uwp;
+using Microsoft.Toolkit.Uwp.UI.Triggers;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System.Threading.Tasks;
+using Windows.UI.Xaml.Controls;
+
+namespace UnitTests.UWP.UI.Triggers
+{
+    [TestClass]
+    [TestCategory("Test_ControlSizeTrigger")]
+    public class Test_ControlSizeTrigger : VisualUITestBase
+    {
+        [DataTestMethod]
+        [DataRow(450, 450, true)]
+        [DataRow(400, 400, true)]
+        [DataRow(500, 500, false)]
+        [DataRow(399, 400, false)]
+        [DataRow(400, 399, false)]
+        public async Task ControlSizeTriggerTest(double width, double height, bool expectedResult)
+        {
+            await App.DispatcherQueue.EnqueueAsync(() =>
+            {
+                Grid grid = CreateGrid(width, height);
+                var trigger = new ControlSizeTrigger();
+
+                trigger.TargetElement = grid;
+                trigger.MaxHeight = 500;
+                trigger.MinHeight = 400;
+                trigger.MaxWidth = 500;
+                trigger.MinWidth = 400;
+
+                Assert.AreEqual(expectedResult, trigger.IsActive);
+            });
+        }
+
+        private Grid CreateGrid(double width, double height)
+        {
+            var grid = new Grid()
+            {
+                Height = height,
+                Width = width
+            };
+            grid.Measure(new Windows.Foundation.Size(1000, 1000));
+            grid.Arrange(new Windows.Foundation.Rect(0, 0, 1000, 1000));
+            grid.UpdateLayout();
+
+            return grid;
+        }
+    }
+}

UnitTests/UnitTests.UWP/UnitTests.UWP.csproj

@@ -250,6 +250,7 @@
     <Compile Include="UI\Extensions\Test_VisualExtensions.cs" />
     <Compile Include="UI\Person.cs" />
     <Compile Include="UI\Test_AdvancedCollectionView.cs" />
+    <Compile Include="UI\Triggers\Test_ControlSizeTrigger.cs" />
     <Compile Include="VisualUITestBase.cs" />
   </ItemGroup>
   <ItemGroup>