Fix flaky XAML tests.

Make tests that load XAML inherit from `XamlTestBase` which ensures that `Avalonia.Markup` is loaded.

tests/Avalonia.Markup.Xaml.UnitTests/Converters/ConverterTests.cs

@@ -3,7 +3,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Converters
 {
-    public class ConverterTests
+    public class ConverterTests : XamlTestBase
     {
         [Fact]
         public void Bug_2228_Relative_Uris_Should_Be_Correctly_Parsed()

tests/Avalonia.Markup.Xaml.UnitTests/Converters/NullableConverterTests.cs

@@ -11,7 +11,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.Converters
         public Orientation? Orientation { get; set; }
     }
     
-    public class NullableConverterTests
+    public class NullableConverterTests : XamlTestBase
     {
         [Fact]
         public void Nullable_Types_Should_Still_Be_Converted_Properly()

tests/Avalonia.Markup.Xaml.UnitTests/Converters/ValueConverterTests.cs

@@ -8,7 +8,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Converters
 {
-    public class ValueConverterTests
+    public class ValueConverterTests : XamlTestBase
     {
         [Fact]
         public void ValueConverter_Special_Values_Work()

tests/Avalonia.Markup.Xaml.UnitTests/Data/BindingTests.cs

@@ -8,7 +8,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Data
 {
-    public class BindingTests
+    public class BindingTests : XamlTestBase
     {
         [Fact]
         public void Binding_With_Null_Path_Works()

tests/Avalonia.Markup.Xaml.UnitTests/Data/BindingTests_Method.cs

@@ -10,7 +10,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Data
 {
-    public class BindingTests_Method
+    public class BindingTests_Method : XamlTestBase
     {
         [Fact]
         public void Binding_Method_To_Command_Works()
@@ -102,4 +102,4 @@ namespace Avalonia.Markup.Xaml.UnitTests.Data
             public string Value { get; private set; } = "Not called";
         }
     }
-}
+}

tests/Avalonia.Markup.Xaml.UnitTests/Data/BindingTests_TemplatedParent.cs

@@ -10,7 +10,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Data
 {
-    public class BindingTests_TemplatedParent
+    public class BindingTests_TemplatedParent : XamlTestBase
     {
         [Fact]
         public void TemplateBinding_With_Null_Path_Works()

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs

@@ -10,7 +10,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 {
-    public class BindingExtensionTests
+    public class BindingExtensionTests : XamlTestBase
     {
 
         [Fact]

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/DynamicResourceExtensionTests.cs

@@ -15,7 +15,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 {
-    public class DynamicResourceExtensionTests
+    public class DynamicResourceExtensionTests : XamlTestBase
     {
         [Fact]
         public void DynamicResource_Can_Be_Assigned_To_Property()

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/ResourceIncludeTests.cs

@@ -8,7 +8,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MakrupExtensions
 {
     public class ResourceIncludeTests
     {
-        public class StaticResourceExtensionTests
+        public class StaticResourceExtensionTests : XamlTestBase
         {
             [Fact]
             public void ResourceInclude_Loads_ResourceDictionary()
@@ -52,4 +52,4 @@ namespace Avalonia.Markup.Xaml.UnitTests.MakrupExtensions
             }
         }
     }
-}
+}

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/StaticResourceExtensionTests.cs

@@ -14,7 +14,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 {
-    public class StaticResourceExtensionTests
+    public class StaticResourceExtensionTests : XamlTestBase
     {
         [Fact]
         public void StaticResource_Can_Be_Assigned_To_Property()

tests/Avalonia.Markup.Xaml.UnitTests/StyleTests.cs

@@ -12,7 +12,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests
 {
-    public class StyleTests
+    public class StyleTests : XamlTestBase
     {
         [Fact]
         public void Binding_Should_Be_Assigned_To_Setter_Value_Instead_Of_Bound()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BasicTests.cs

@@ -22,7 +22,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
-    public class BasicTests
+    public class BasicTests : XamlTestBase
     {
         [Fact]
         public void Simple_Property_Is_Set()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BindingTests.cs

@@ -8,7 +8,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
-    public class BindingTests
+    public class BindingTests : XamlTestBase
     {
         [Fact]
         public void Binding_To_DataContext_Works()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BindingTests_RelativeSource.cs

@@ -8,7 +8,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
-    public class BindingTests_RelativeSource
+    public class BindingTests_RelativeSource : XamlTestBase
     {
         [Fact]
         public void Binding_To_DataContext_Works()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlBindingTests.cs

@@ -4,14 +4,13 @@
 using System.Collections.Generic;
 using Avalonia.Controls;
 using Avalonia.Controls.Primitives;
-using Avalonia.Layout;
 using Avalonia.Logging;
 using Avalonia.UnitTests;
 using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
-    public class ControlBindingTests
+    public class ControlBindingTests : XamlTestBase
     {
         [Fact]
         public void Binding_ProgressBar_Value_To_Invalid_Value_Uses_FallbackValue()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/DataTemplateTests.cs

@@ -8,7 +8,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
-    public class DataTemplateTests
+    public class DataTemplateTests : XamlTestBase
     {
         [Fact]
         public void DataTemplate_Can_Contain_Name()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/EventTests.cs

@@ -9,7 +9,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
-    public class EventTests
+    public class EventTests : XamlTestBase
     {
         [Fact]
         public void Event_Is_Attached()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/StyleTests.cs

@@ -12,7 +12,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
-    public class StyleTests
+    public class StyleTests : XamlTestBase
     {
         [Fact]
         public void Color_Can_Be_Added_To_Style_Resources()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/TreeDataTemplateTests.cs

@@ -4,14 +4,13 @@
 using System.Linq;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
-using Avalonia.Markup.Data;
 using Avalonia.Markup.Xaml.Templates;
 using Avalonia.UnitTests;
 using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
-    public class TreeDataTemplateTests
+    public class TreeDataTemplateTests : XamlTestBase
     {
         [Fact]
         public void Binding_Should_Be_Assigned_To_ItemsSource_Instead_Of_Bound()

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/XamlIlTests.cs

@@ -5,10 +5,7 @@ using System.Globalization;
 using System.Linq;
 using System.Runtime.CompilerServices;
 using Avalonia.Controls;
-using Avalonia.Controls.Presenters;
 using Avalonia.Data.Converters;
-using Avalonia.Input;
-using Avalonia.Interactivity;
 using Avalonia.Media;
 using Avalonia.Threading;
 using Avalonia.UnitTests;
@@ -18,7 +15,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests
 {
-    public class XamlIlTests
+    public class XamlIlTests : XamlTestBase
     {
         [Fact]
         public void Binding_Button_IsPressed_ShouldWork()

tests/Avalonia.Markup.Xaml.UnitTests/XamlTestBase.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Avalonia.Data;
+
+namespace Avalonia.Markup.Xaml.UnitTests
+{
+    public class XamlTestBase
+    {
+        public XamlTestBase()
+        {
+            // Ensure necessary assemblies are loaded.
+            var _ = typeof(TemplateBinding);
+        }
+    }
+}