Move some tests.

Tests for `AvaloniaObject.IsSet`  were in the `Metadata` test class, though `IsSet` has nothing to do with metadata. Moved them into `SetValue` which is more relevant.

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_Metadata.cs

@@ -15,35 +15,6 @@ namespace Avalonia.Base.UnitTests
             p = AttachedOwner.AttachedProperty;
         }
 
-        [Fact]
-        public void IsSet_Returns_False_For_Unset_Property()
-        {
-            var target = new Class1();
-
-            Assert.False(target.IsSet(Class1.FooProperty));
-        }
-
-        [Fact]
-        public void IsSet_Returns_False_For_Set_Property()
-        {
-            var target = new Class1();
-
-            target.SetValue(Class1.FooProperty, "foo");
-
-            Assert.True(target.IsSet(Class1.FooProperty));
-        }
-
-        [Fact]
-        public void IsSet_Returns_False_For_Cleared_Property()
-        {
-            var target = new Class1();
-
-            target.SetValue(Class1.FooProperty, "foo");
-            target.SetValue(Class1.FooProperty, AvaloniaProperty.UnsetValue);
-
-            Assert.False(target.IsSet(Class1.FooProperty));
-        }
-
         private class Class1 : AvaloniaObject
         {
             public static readonly StyledProperty<string> FooProperty =

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_SetValue.cs

@@ -39,6 +39,35 @@ namespace Avalonia.Base.UnitTests
             Assert.Equal(1, raised);
         }
 
+        [Fact]
+        public void IsSet_Returns_False_For_Unset_Property()
+        {
+            var target = new Class1();
+
+            Assert.False(target.IsSet(Class1.FooProperty));
+        }
+
+        [Fact]
+        public void IsSet_Returns_False_For_Set_Property()
+        {
+            var target = new Class1();
+
+            target.SetValue(Class1.FooProperty, "foo");
+
+            Assert.True(target.IsSet(Class1.FooProperty));
+        }
+
+        [Fact]
+        public void IsSet_Returns_False_For_Cleared_Property()
+        {
+            var target = new Class1();
+
+            target.SetValue(Class1.FooProperty, "foo");
+            target.SetValue(Class1.FooProperty, AvaloniaProperty.UnsetValue);
+
+            Assert.False(target.IsSet(Class1.FooProperty));
+        }
+
         [Fact]
         public void SetValue_Sets_Value()
         {