Added some style tests.

Perspex.UnitTests/Perspex.UnitTests.csproj

@@ -65,6 +65,7 @@
     <Compile Include="PerspexPropertyTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="PerspexObjectTests.cs" />
+    <Compile Include="StyleTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Perspex\Perspex.csproj">

Perspex.UnitTests/StyleTests.cs

@@ -0,0 +1,91 @@
+// -----------------------------------------------------------------------
+// <copyright file="StyleTests.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.UnitTests
+{
+    using System;
+    using System.Collections.Generic;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+    using Perspex.Controls;
+
+    [TestClass]
+    public class StyleTests
+    {
+        [TestMethod]
+        public void Style_Should_Update_And_Restore_Value()
+        {
+            Style style = new Style
+            {
+                Selector = x => x.Select<TextBlock>().Class("foo"),
+                Setters = new[]
+                {
+                    new Setter
+                    {
+                        Property = TextBlock.TextProperty,
+                        Value = "Foo",
+                    }
+                },
+            };
+
+            TextBlock textBlock = new TextBlock
+            {
+                Text = "Original",
+            };
+
+            style.Attach(textBlock);
+            Assert.AreEqual("Original", textBlock.Text);
+            textBlock.Classes.Add("foo");
+            Assert.AreEqual("Foo", textBlock.Text);
+            textBlock.Classes.Remove("foo");
+            Assert.AreEqual("Original", textBlock.Text);
+        }
+
+        [TestMethod]
+        public void Later_Styles_Should_Override_Earlier()
+        {
+            Style style1 = new Style
+            {
+                Selector = x => x.Select<TextBlock>().Class("foo"),
+                Setters = new[]
+                {
+                    new Setter
+                    {
+                        Property = TextBlock.TextProperty,
+                        Value = "Foo",
+                    }
+                },
+            };
+
+            Style style2 = new Style
+            {
+                Selector = x => x.Select<TextBlock>().Class("foo"),
+                Setters = new[]
+                {
+                    new Setter
+                    {
+                        Property = TextBlock.TextProperty,
+                        Value = "Bar",
+                    }
+                },
+            };
+
+            TextBlock textBlock = new TextBlock
+            {
+                Text = "Original",
+            };
+
+            List<string> values = new List<string>();
+            textBlock.GetObservable(TextBlock.TextProperty).Subscribe(x => values.Add(x));
+
+            style1.Attach(textBlock);
+            style2.Attach(textBlock);
+            textBlock.Classes.Add("foo");
+            textBlock.Classes.Remove("foo");
+
+            CollectionAssert.AreEqual(new[] { "Original", "Bar", "Original" }, values);
+        }
+    }
+}

Perspex/Setter.cs

@@ -63,7 +63,7 @@ namespace Perspex
 
         internal SetterSubject CreateSubject(Control control)
         {
-            object oldValue = control.ExtractBinding(this.Property) ?? control.GetValue(this.Property);
+            object oldValue = control.GetValue(this.Property);
             return new SetterSubject(control, this.Value, oldValue);
         }
     }