Warning fixes: '25 winter wave (#18103)

* Use TryGetValue in UnicodeEnumsGenerator

* Suppress incorrect CA2256 in Win32.Automation

* Fix xUnit analyzer warnings

* Misc warning fixes

* Ignore some obsolete warnings

samples/UnloadableAssemblyLoadContext/UnloadableAssemblyLoadContext/UnloadableAssemblyLoadContext.csproj

@@ -1,13 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
-    <PropertyGroup>
-        <OutputType>WinExe</OutputType>
-        <TargetFramework>net7.0</TargetFramework>
-        <Nullable>enable</Nullable>
-        <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
-        <ApplicationManifest>app.manifest</ApplicationManifest>
-        <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
-      <IncludeAvaloniaGenerators>true</IncludeAvaloniaGenerators>
-    </PropertyGroup>
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>$(AvsCurrentTargetFramework)</TargetFramework>
+    <Nullable>enable</Nullable>
+    <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
+    <ApplicationManifest>app.manifest</ApplicationManifest>
+    <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
+    <IncludeAvaloniaGenerators>true</IncludeAvaloniaGenerators>
+  </PropertyGroup>
 
   <ItemGroup>
     <Compile Update="**\*.xaml.cs" DependentUpon="%(Filename)" />
@@ -18,6 +19,7 @@
     <Import Project="..\..\..\build\BuildTargets.targets" Condition="Exists('..\..\..\build\BuildTargets.targets')" />
     <Import Project="..\..\..\build\SourceGenerators.props" />
   </ImportGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\..\..\packages\Avalonia\Avalonia.csproj" />
     <ProjectReference Include="..\..\..\src\Avalonia.Base\Avalonia.Base.csproj" />
@@ -26,4 +28,5 @@
     <ProjectReference Include="..\..\..\src\Avalonia.Fonts.Inter\Avalonia.Fonts.Inter.csproj" />
     <ProjectReference Include="..\..\..\src\Avalonia.Themes.Fluent\Avalonia.Themes.Fluent.csproj" />
     </ItemGroup>
+
 </Project>

samples/UnloadableAssemblyLoadContext/UnloadableAssemblyLoadContextPlug/UnloadableAssemblyLoadContextPlug.csproj

@@ -1,17 +1,19 @@
 <Project Sdk="Microsoft.NET.Sdk">
-    <PropertyGroup>
-        <TargetFramework>net7.0</TargetFramework>
-        <Nullable>enable</Nullable>
-        <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
-        <ApplicationManifest>app.manifest</ApplicationManifest>
-        <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
-      <AssemblyName>UnloadableAssemblyLoadContextPlug</AssemblyName>
-      <RootNamespace>UnloadableAssemblyLoadContextPlug</RootNamespace>
-    </PropertyGroup>
 
-    <ItemGroup>
-        <AvaloniaResource Include="Assets\**"/>
-    </ItemGroup>
+  <PropertyGroup>
+    <TargetFramework>$(AvsCurrentTargetFramework)</TargetFramework>
+    <Nullable>enable</Nullable>
+    <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
+    <ApplicationManifest>app.manifest</ApplicationManifest>
+    <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
+    <AssemblyName>UnloadableAssemblyLoadContextPlug</AssemblyName>
+    <RootNamespace>UnloadableAssemblyLoadContextPlug</RootNamespace>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <AvaloniaResource Include="Assets\**"/>
+  </ItemGroup>
+
   <ItemGroup>
     <Compile Update="**\*.xaml.cs">
       <DependentUpon>%(Filename)</DependentUpon>
@@ -19,33 +21,27 @@
     <AvaloniaResource Include="**\*.xaml">
       <SubType>Designer</SubType>
     </AvaloniaResource>
-    <AvaloniaResource Include="Assets\*" />
-    <AvaloniaResource Include="Assets\Fonts\*" />
+    <AvaloniaResource Include="Assets\*"/>
+    <AvaloniaResource Include="Assets\Fonts\*"/>
   </ItemGroup>
 
   <ImportGroup>
-    <Import Project="..\..\..\build\BuildTargets.targets" Condition="Exists('..\..\..\build\BuildTargets.targets')" />
-    <Import Project="..\..\..\build\SourceGenerators.props" />
+    <Import Project="..\..\..\build\BuildTargets.targets" Condition="Exists('..\..\..\build\BuildTargets.targets')"/>
+    <Import Project="..\..\..\build\SourceGenerators.props"/>
   </ImportGroup>
 
-
-
-
   <ItemGroup>
-    <ProjectReference Include="..\..\..\packages\Avalonia\Avalonia.csproj" />
-    <ProjectReference Include="..\..\..\src\Avalonia.Desktop\Avalonia.Desktop.csproj" />
-    <ProjectReference Condition="'$(Configuration)' == 'Debug'" Include="..\..\..\src\Avalonia.Diagnostics\Avalonia.Diagnostics.csproj" />
-    <ProjectReference Include="..\..\..\src\Avalonia.Fonts.Inter\Avalonia.Fonts.Inter.csproj" />
-    <ProjectReference Include="..\..\..\src\Avalonia.ReactiveUI\Avalonia.ReactiveUI.csproj" />
-    <ProjectReference Include="..\..\..\src\Avalonia.Themes.Fluent\Avalonia.Themes.Fluent.csproj" />
-    <ProjectReference Include="..\..\..\src\Markup\Avalonia.Markup.Xaml.Loader\Avalonia.Markup.Xaml.Loader.csproj" />
+    <ProjectReference Include="..\..\..\packages\Avalonia\Avalonia.csproj"/>
+    <ProjectReference Include="..\..\..\src\Avalonia.Desktop\Avalonia.Desktop.csproj"/>
+    <ProjectReference Condition="'$(Configuration)' == 'Debug'" Include="..\..\..\src\Avalonia.Diagnostics\Avalonia.Diagnostics.csproj"/>
+    <ProjectReference Include="..\..\..\src\Avalonia.Fonts.Inter\Avalonia.Fonts.Inter.csproj"/>
+    <ProjectReference Include="..\..\..\src\Avalonia.ReactiveUI\Avalonia.ReactiveUI.csproj"/>
+    <ProjectReference Include="..\..\..\src\Avalonia.Themes.Fluent\Avalonia.Themes.Fluent.csproj"/>
+    <ProjectReference Include="..\..\..\src\Markup\Avalonia.Markup.Xaml.Loader\Avalonia.Markup.Xaml.Loader.csproj"/>
   </ItemGroup>
 
+  <ItemGroup>
+    <UpToDateCheckInput Remove="Views\MainWindow.axaml"/>
+  </ItemGroup>
 
-    <ItemGroup>
-      <UpToDateCheckInput Remove="Views\MainWindow.axaml" />
-    </ItemGroup>
-
-
-  
 </Project>

samples/XEmbedSample/HarfbuzzWorkaround.cs

@@ -46,7 +46,7 @@ public unsafe class HarfbuzzWorkaround
         var libraryPathBytes = Marshal.AllocHGlobal(4096);
         var handle = NativeLibrary.Load("libHarfBuzzSharp", typeof(HarfBuzzSharp.Blob).Assembly, null);
         dlinfo(handle, RTLD_DI_ORIGIN, libraryPathBytes);
-        var libraryOrigin = Marshal.PtrToStringUTF8(libraryPathBytes);
+        var libraryOrigin = Marshal.PtrToStringUTF8(libraryPathBytes) ?? string.Empty;
         Marshal.FreeHGlobal(libraryPathBytes);
         var libraryPath = Path.Combine(libraryOrigin, "libHarfBuzzSharp.so");
         
@@ -63,4 +63,4 @@ public unsafe class HarfbuzzWorkaround
         });
         
     }
-}
+}

samples/XEmbedSample/Program.cs

@@ -4,7 +4,9 @@ using Avalonia.Controls.Primitives;
 using Avalonia.Media;
 using ControlCatalog;
 using ControlCatalog.Models;
+using Gdk;
 using Gtk;
+using Window = Gtk.Window;
 
 namespace XEmbedSample;
 
@@ -31,7 +33,7 @@ class Program
 
 
         var w = new Gtk.Window("XEmbed Test Window");
-        var socket = new AvaloniaXEmbedGtkSocket(w.StyleContext.GetBackgroundColor(StateFlags.Normal))
+        var socket = new AvaloniaXEmbedGtkSocket(GetBackgroundColor(w))
         {
             Content = new ScrollViewer()
             {
@@ -60,4 +62,11 @@ class Program
         Gtk.Application.Run();
         
     }
-}
+
+    private static RGBA GetBackgroundColor(Window window)
+    {
+#pragma warning disable CS0612 // Type or member is obsolete; OK for a sample.
+        return window.StyleContext.GetBackgroundColor(StateFlags.Normal);
+#pragma warning restore CS0612 // Type or member is obsolete
+    }
+}

samples/XEmbedSample/SocketEx.cs

@@ -14,8 +14,8 @@ public class AvaloniaXEmbedGtkSocket : Gtk.Socket
         _backgroundColor = backgroundColor;
     }
     
-    private object _content;
-    public object Content
+    private object? _content;
+    public object? Content
     {
         get => _content;
         set
@@ -61,4 +61,4 @@ public class AvaloniaXEmbedGtkSocket : Gtk.Socket
         _avaloniaPlug = null;
         base.OnDestroyed();
     }
-}
+}

src/Avalonia.Base/Media/TextFormatting/Unicode/PropertyValueAliasHelper.cs

@@ -182,11 +182,11 @@ namespace Avalonia.Media.TextFormatting.Unicode
 
         public static string GetTag(Script script)
         {
-            if(!s_scriptToTag.ContainsKey(script))
+            if (!s_scriptToTag.TryGetValue(script, out var value))
             {
                 return "Zzzz";
             }
-            return s_scriptToTag[script];
+            return value;
         }
 
         private static readonly Dictionary<string, Script> s_tagToScript = 
@@ -367,11 +367,11 @@ namespace Avalonia.Media.TextFormatting.Unicode
 
         public static Script GetScript(string tag)
         {
-            if(!s_tagToScript.ContainsKey(tag))
+            if (!s_tagToScript.TryGetValue(tag, out var value))
             {
                 return Script.Unknown;
             }
-            return s_tagToScript[tag];
+            return value;
         }
 
         private static readonly Dictionary<string, GeneralCategory> s_tagToGeneralCategory = 
@@ -418,11 +418,11 @@ namespace Avalonia.Media.TextFormatting.Unicode
 
         public static GeneralCategory GetGeneralCategory(string tag)
         {
-            if(!s_tagToGeneralCategory.ContainsKey(tag))
+            if (!s_tagToGeneralCategory.TryGetValue(tag, out var value))
             {
                 return GeneralCategory.Other;
             }
-            return s_tagToGeneralCategory[tag];
+            return value;
         }
 
         private static readonly Dictionary<string, LineBreakClass> s_tagToLineBreakClass = 
@@ -479,11 +479,11 @@ namespace Avalonia.Media.TextFormatting.Unicode
 
         public static LineBreakClass GetLineBreakClass(string tag)
         {
-            if(!s_tagToLineBreakClass.ContainsKey(tag))
+            if (!s_tagToLineBreakClass.TryGetValue(tag, out var value))
             {
                 return LineBreakClass.Unknown;
             }
-            return s_tagToLineBreakClass[tag];
+            return value;
         }
 
         private static readonly Dictionary<string, BidiPairedBracketType> s_tagToBidiPairedBracketType = 
@@ -495,11 +495,11 @@ namespace Avalonia.Media.TextFormatting.Unicode
 
         public static BidiPairedBracketType GetBidiPairedBracketType(string tag)
         {
-            if(!s_tagToBidiPairedBracketType.ContainsKey(tag))
+            if (!s_tagToBidiPairedBracketType.TryGetValue(tag, out var value))
             {
                 return BidiPairedBracketType.None;
             }
-            return s_tagToBidiPairedBracketType[tag];
+            return value;
         }
 
         private static readonly Dictionary<string, BidiClass> s_tagToBidiClass = 
@@ -531,11 +531,11 @@ namespace Avalonia.Media.TextFormatting.Unicode
 
         public static BidiClass GetBidiClass(string tag)
         {
-            if(!s_tagToBidiClass.ContainsKey(tag))
+            if (!s_tagToBidiClass.TryGetValue(tag, out var value))
             {
                 return BidiClass.LeftToRight;
             }
-            return s_tagToBidiClass[tag];
+            return value;
         }
 
     }

src/Avalonia.Controls/TextBox.cs

@@ -1,6 +1,7 @@
 using Avalonia.Input.Platform;
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Avalonia.Reactive;
 using Avalonia.Controls.Presenters;
@@ -629,6 +630,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// Gets or sets the text selected in the TextBox
         /// </summary>
+        [AllowNull]
         public string SelectedText
         {
             get => GetSelection();

src/Headless/Avalonia.Headless/HeadlessPlatformStubs.cs

@@ -73,7 +73,11 @@ namespace Avalonia.Headless
                 if (format == DataFormats.Files && _data is not null)
                     return _data.GetFiles();
                 if (format == DataFormats.FileNames && _data is not null)
+                {
+#pragma warning disable CS0618 // Type or member is obsolete
                     return _data.GetFileNames();
+#pragma warning restore CS0618 // Type or member is obsolete
+                }
                 else
                     return (object?)_data;
             });

src/Windows/Avalonia.Win32.Automation/GlobalSuppressions.cs

@@ -0,0 +1,11 @@
+using System.Diagnostics.CodeAnalysis;
+
+// Until https://github.com/dotnet/runtime/issues/90922 is resolved, this is the only way
+// to suppress CA2256 in the generated code.
+[assembly: SuppressMessage(
+    "Usage",
+    "CA2256:All members declared in parent interfaces must have an implementation in a DynamicInterfaceCastableImplementation-attributed interface",
+    Justification = "Generated code and analyzer ignores that it is generated AND partial",
+    Scope = "type",
+    Target = "~T:InterfaceImplementation")
+]

tests/Avalonia.Base.UnitTests/Animation/AnimationIterationTests.cs

@@ -317,7 +317,7 @@ namespace Avalonia.Base.UnitTests.Animation
         }
 
         [Fact]
-        public void Cancellation_Should_Stop_Animation()
+        public async Task Cancellation_Should_Stop_Animation()
         {
             var keyframe1 = new KeyFrame()
             {
@@ -364,7 +364,7 @@ namespace Avalonia.Base.UnitTests.Animation
             clock.Step(TimeSpan.FromSeconds(2));
             clock.Step(TimeSpan.FromSeconds(3));
 
-            animationRun.Wait();
+            await animationRun;
 
             clock.Step(TimeSpan.FromSeconds(6));
             Assert.True(animationRun.IsCompleted);
@@ -404,7 +404,7 @@ namespace Avalonia.Base.UnitTests.Animation
         }
 
         [Fact]
-        public void Cancellation_Of_Completed_Animation_Does_Not_Fail()
+        public async Task Cancellation_Of_Completed_Animation_Does_Not_Fail()
         {
             var keyframe1 = new KeyFrame()
             {
@@ -450,12 +450,12 @@ namespace Avalonia.Base.UnitTests.Animation
             Assert.Equal(2, propertyChangedCount);
 
             cancellationTokenSource.Cancel();
-            animationRun.Wait();
+            await animationRun;
         }
 
         // https://github.com/AvaloniaUI/Avalonia/issues/12582
         [Fact]
-        public void Interpolator_Is_Not_Called_After_Last_Iteration()
+        public async Task Interpolator_Is_Not_Called_After_Last_Iteration()
         {
             var animator = new FakeAnimator();
 
@@ -511,7 +511,7 @@ namespace Avalonia.Base.UnitTests.Animation
             Assert.Equal(3, animator.CallCount);
             Assert.Equal(1.0d, animator.LastProgress);
 
-            animationRun.Wait();
+            await animationRun;
         }
 
         [Theory]

tests/Avalonia.Base.UnitTests/Collections/AvaloniaListTests.cs

@@ -554,7 +554,7 @@ namespace Avalonia.Base.UnitTests.Collections
         }
 
         /// <summary>
-        /// Assert that <see cref="items"/> emits <see cref="expectedEvents"/> when performing <see cref="action"/>.
+        ///  Assert that <paramref name="items"/> emits <paramref name="expectedEvents"/> when performing <paramref name="action"/>.
         /// </summary>
         /// <param name="items">The event source.</param>
         /// <param name="action">The action to perform.</param>

tests/Avalonia.Base.UnitTests/DispatcherTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -462,6 +463,7 @@ public partial class DispatcherTests
     }
 
     [Fact]
+    [SuppressMessage("Usage", "xUnit1031:Do not use blocking task operations in test method", Justification = "Tests the dispatcher itself")]
     public void DispatcherInvokeAsyncUnwrapsTasks()
     {
         int asyncMethodStage = 0;

tests/Avalonia.Base.UnitTests/Media/TextFormatting/BiDiClassTests.cs

@@ -1,4 +1,5 @@
-using System.Linq;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
 using System.Runtime.InteropServices;
 using System.Text;
 using Avalonia.Media.TextFormatting.Unicode;
@@ -18,6 +19,7 @@ namespace Avalonia.Visuals.UnitTests.Media.TextFormatting
 
         [Theory(Skip = "Only run when the Unicode spec changes.")]
         [ClassData(typeof(BiDiClassTestDataGenerator))]
+        [SuppressMessage("Usage", "xUnit1026:Theory methods should use all of their parameters", Justification = "Parameters match BiDi fields")]
         public void Should_Resolve(
             int lineNumber,
             int[] codePoints,

tests/Avalonia.Base.UnitTests/Media/TextFormatting/UnicodeEnumsGenerator.cs

@@ -447,11 +447,11 @@ namespace Avalonia.Base.UnitTests.Media.TextFormatting
 
             writer.WriteLine($"        public static string GetTag({typeName} {typeName.ToLower()})");
             writer.WriteLine("        {");
-            writer.WriteLine($"            if(!s_{typeName.ToLower()}ToTag.ContainsKey({typeName.ToLower()}))");
+            writer.WriteLine($"            if (!s_{typeName.ToLower()}ToTag.TryGetValue({typeName.ToLower()}, out var value))");
             writer.WriteLine("            {");
             writer.WriteLine($"                return \"{defaultValue}\";");
             writer.WriteLine("            }");
-            writer.WriteLine($"            return s_{typeName.ToLower()}ToTag[{typeName.ToLower()}];");
+            writer.WriteLine($"            return value;");
             writer.WriteLine("        }");
 
             writer.WriteLine();
@@ -474,11 +474,11 @@ namespace Avalonia.Base.UnitTests.Media.TextFormatting
 
             writer.WriteLine($"        public static {typeName} Get{typeName}(string tag)");
             writer.WriteLine("        {");
-            writer.WriteLine($"            if(!s_tagTo{typeName}.ContainsKey(tag))");
+            writer.WriteLine($"            if (!s_tagTo{typeName}.TryGetValue(tag, out var value))");
             writer.WriteLine("            {");
             writer.WriteLine($"                return {typeName}.{defaultValue};");
             writer.WriteLine("            }");
-            writer.WriteLine($"            return s_tagTo{typeName}[tag];");
+            writer.WriteLine($"            return value;");
             writer.WriteLine("        }");
 
             writer.WriteLine();

tests/Avalonia.Base.UnitTests/Utilities/StringTokenizerTests.cs

@@ -2,6 +2,8 @@
 using Avalonia.Utilities;
 using Xunit;
 
+#pragma warning disable CS0618 // Type or member is obsolete
+
 namespace Avalonia.Base.UnitTests.Utilities
 {
     public class StringTokenizerTests

tests/Avalonia.Build.Tasks.UnitTest/CompileAvaloniaXamlTaskTest.cs

@@ -30,7 +30,7 @@ public class CompileAvaloniaXamlTaskTest
             ProjectDirectory = Directory.GetCurrentDirectory(),
             VerifyIl = true
         }.Execute();
-        Assert.Equal(0, engine.Errors.Count);
+        Assert.Empty(engine.Errors);
     }
 
 

tests/Avalonia.Controls.DataGrid.UnitTests/Collections/ComparerTests.cs

@@ -219,5 +219,8 @@ public class NoStringTypeComparerTests
             }
             return false;
         }
+
+        public override int GetHashCode()
+            => Prop;
     }
 }

tests/Avalonia.Controls.UnitTests/GridLengthTests.cs

@@ -107,7 +107,7 @@ namespace Avalonia.Controls.UnitTests
         [InlineData(1.2d, GridUnitType.Pixel, "1.2")]
         [InlineData(1.2d, GridUnitType.Star, "1.2*")]
         [InlineData(1.2d, GridUnitType.Auto, "Auto")]
-        public async void ToString_AllCulture_Should_Pass(double d, GridUnitType type, string result)
+        public async Task ToString_AllCulture_Should_Pass(double d, GridUnitType type, string result)
         {
             List<CultureInfo> cultureInfos = CultureInfo.GetCultures(CultureTypes.AllCultures).ToList();
             GridLength length = new GridLength(d, type);

tests/Avalonia.Controls.UnitTests/MaskedTextBoxTests.cs

@@ -804,7 +804,7 @@ namespace Avalonia.Controls.UnitTests
         [InlineData("abc", "ddd", 3, 0, 2, true, "ddc")]
         [InlineData("abc", "dddd", 4, 1, 3, true, "addd")]
         [InlineData("abc", "ddddd", 5, 3, 3, true, "abcdd")]
-        public void MaxLength_Works_Properly(
+        public async Task MaxLength_Works_Properly(
             string initalText,
             string textInput,
             int maxLength,
@@ -838,10 +838,10 @@ namespace Avalonia.Controls.UnitTests
 
                 if (fromClipboard)
                 {
-                    topLevel.Clipboard?.SetTextAsync(textInput).GetAwaiter().GetResult();
+                    await topLevel.Clipboard!.SetTextAsync(textInput);
 
                     RaiseKeyEvent(target, Key.V, KeyModifiers.Control);
-                    topLevel.Clipboard?.ClearAsync().GetAwaiter().GetResult();
+                    await topLevel.Clipboard!.ClearAsync();
                 }
                 else
                 {

tests/Avalonia.Controls.UnitTests/Platform/ScreensTests.cs

@@ -102,7 +102,7 @@ public class ScreensTests : ScopedTestBase
     }
 
     [Fact]
-    public void Should_Raise_Event_When_Screen_Changed_From_Another_Thread()
+    public async Task Should_Raise_Event_When_Screen_Changed_From_Another_Thread()
     {
         using var _ = UnitTestApplication.Start(TestServices.MockThreadingInterface);
 
@@ -114,7 +114,7 @@ public class ScreensTests : ScopedTestBase
             hasChangedTimes += 1;
         };
 
-        Task.Run(() => screens.PushNewScreens([1, 2])).Wait();
+        await Task.Run(() => screens.PushNewScreens([1, 2]));
         Dispatcher.UIThread.RunJobs();
 
         Assert.Equal(1, hasChangedTimes);

tests/Avalonia.Controls.UnitTests/TextBoxTests.cs

@@ -1,3 +1,5 @@
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Reactive.Linq;
@@ -837,7 +839,7 @@ namespace Avalonia.Controls.UnitTests
         [InlineData("abc", "ddd", 3, 0, 2, true, "ddc")]
         [InlineData("abc", "dddd", 4, 1, 3, true, "addd")]
         [InlineData("abc", "ddddd", 5, 3, 3, true, "abcdd")]
-        public void MaxLength_Works_Properly(
+        public async Task MaxLength_Works_Properly(
             string initalText,
             string textInput,
             int maxLength,
@@ -870,10 +872,10 @@ namespace Avalonia.Controls.UnitTests
                 
                 if (fromClipboard)
                 {
-                    topLevel.Clipboard?.SetTextAsync(textInput).GetAwaiter().GetResult();
+                    await topLevel.Clipboard!.SetTextAsync(textInput);
 
                     RaiseKeyEvent(target, Key.V, KeyModifiers.Control);
-                    topLevel.Clipboard?.ClearAsync().GetAwaiter().GetResult();
+                    await topLevel.Clipboard!.ClearAsync();
                 }
                 else
                 {
@@ -936,7 +938,7 @@ namespace Avalonia.Controls.UnitTests
                     SelectionEnd = 3,
                 };
 
-                var values = new List<string>();
+                var values = new List<string?>();
                 target.GetObservable(TextBox.TextProperty).Subscribe(x => values.Add(x));
 
                 target.SelectedText = "A";
@@ -960,7 +962,7 @@ namespace Avalonia.Controls.UnitTests
                     SelectionEnd = 3,
                 };
 
-                var values = new List<string>();
+                var values = new List<string?>();
                 target.GetObservable(TextBox.TextProperty).Subscribe(x => values.Add(x));
 
                 RaiseTextEvent(target, "A");
@@ -1008,7 +1010,7 @@ namespace Avalonia.Controls.UnitTests
         }
 
         [Fact]
-        public void Should_Fullfill_MaxLines_Contraint()
+        public async Task Should_Fullfill_MaxLines_Contraint()
         {
             using (UnitTestApplication.Start(Services))
             {
@@ -1034,10 +1036,10 @@ namespace Avalonia.Controls.UnitTests
 
                 var initialHeight = target.DesiredSize.Height;
 
-                topLevel.Clipboard?.SetTextAsync(Environment.NewLine).GetAwaiter().GetResult();
+                await topLevel.Clipboard!.SetTextAsync(Environment.NewLine);
 
                 RaiseKeyEvent(target, Key.V, KeyModifiers.Control);
-                topLevel.Clipboard?.ClearAsync().GetAwaiter().GetResult();
+                await topLevel.Clipboard!.ClearAsync();
 
                 RaiseTextEvent(target, Environment.NewLine);
 
@@ -1075,10 +1077,12 @@ namespace Avalonia.Controls.UnitTests
                 topLevel.LayoutManager.ExecuteInitialLayoutPass();
 
                 var textPresenter = target.FindDescendantOfType<TextPresenter>();
+                Assert.NotNull(textPresenter);
                 Assert.Equal("PART_TextPresenter", textPresenter.Name);
                 Assert.Equal(new Thickness(0), textPresenter.Margin); // Test assumes no margin on TextPresenter
 
                 var scrollViewer = target.FindDescendantOfType<ScrollViewer>();
+                Assert.NotNull(scrollViewer);
                 Assert.Equal("PART_ScrollViewer", scrollViewer.Name);
                 Assert.Equal(maxLines * target.LineHeight, scrollViewer.MaxHeight);
             }
@@ -1111,6 +1115,7 @@ namespace Avalonia.Controls.UnitTests
                 topLevel.LayoutManager.ExecuteInitialLayoutPass();
 
                 var textPresenter = target.FindDescendantOfType<TextPresenter>();
+                Assert.NotNull(textPresenter);
                 Assert.Equal("PART_TextPresenter", textPresenter.Name);
                 var textPresenterMargin = new Thickness(horizontal: 0, vertical: 3);
                 textPresenter.Margin = textPresenterMargin;
@@ -1119,6 +1124,7 @@ namespace Avalonia.Controls.UnitTests
                 target.Measure(Size.Infinity);
 
                 var scrollViewer = target.FindDescendantOfType<ScrollViewer>();
+                Assert.NotNull(scrollViewer);
                 Assert.Equal("PART_ScrollViewer", scrollViewer.Name);
                 Assert.Equal((maxLines * target.LineHeight) + textPresenterMargin.Top + textPresenterMargin.Bottom, scrollViewer.MaxHeight);
             }
@@ -1187,10 +1193,12 @@ namespace Avalonia.Controls.UnitTests
                 topLevel.LayoutManager.ExecuteInitialLayoutPass();
 
                 var textPresenter = target.FindDescendantOfType<TextPresenter>();
+                Assert.NotNull(textPresenter);
                 Assert.Equal("PART_TextPresenter", textPresenter.Name);
                 Assert.Equal(new Thickness(0), textPresenter.Margin); // Test assumes no margin on TextPresenter
 
                 var scrollViewer = target.FindDescendantOfType<ScrollViewer>();
+                Assert.NotNull(scrollViewer);
                 Assert.Equal("PART_ScrollViewer", scrollViewer.Name);
                 Assert.Equal(minLines * target.LineHeight, scrollViewer.MinHeight);
             }
@@ -1223,6 +1231,7 @@ namespace Avalonia.Controls.UnitTests
                 topLevel.LayoutManager.ExecuteInitialLayoutPass();
 
                 var textPresenter = target.FindDescendantOfType<TextPresenter>();
+                Assert.NotNull(textPresenter);
                 Assert.Equal("PART_TextPresenter", textPresenter.Name);
                 var textPresenterMargin = new Thickness(horizontal: 0, vertical: 3);
                 textPresenter.Margin = textPresenterMargin;
@@ -1231,6 +1240,7 @@ namespace Avalonia.Controls.UnitTests
                 target.Measure(Size.Infinity);
 
                 var scrollViewer = target.FindDescendantOfType<ScrollViewer>();
+                Assert.NotNull(scrollViewer);
                 Assert.Equal("PART_ScrollViewer", scrollViewer.Name);
                 Assert.Equal((minLines * target.LineHeight) + textPresenterMargin.Top + textPresenterMargin.Bottom, scrollViewer.MinHeight);
             }
@@ -1541,6 +1551,7 @@ namespace Avalonia.Controls.UnitTests
                 var adorner = new TextBox { Template = CreateTemplate(), Text = "a" };
 
                 var adornerLayer = AdornerLayer.GetAdornerLayer(button);
+                Assert.NotNull(adornerLayer);
                 adornerLayer.Children.Add(adorner);
                 AdornerLayer.SetAdornedElement(adorner, button);
 
@@ -1561,6 +1572,7 @@ namespace Avalonia.Controls.UnitTests
                 };
                 var adorner = new TextBox { Template = CreateTemplate(), Text = "a" };
                 var adornerLayer = AdornerLayer.GetAdornerLayer(button);
+                Assert.NotNull(adornerLayer);
 
                 root.Measure(new Size(10, 10));
 
@@ -1780,7 +1792,7 @@ namespace Avalonia.Controls.UnitTests
         private class Class1 : NotifyingBase
         {
             private int _foo;
-            private string _bar;
+            private string? _bar;
 
             public int Foo
             {
@@ -1788,7 +1800,7 @@ namespace Avalonia.Controls.UnitTests
                 set { _foo = value; RaisePropertyChanged(); }
             }
 
-            public string Bar
+            public string? Bar
             {
                 get { return _bar; }
                 set { _bar = value; RaisePropertyChanged(); }
@@ -1797,11 +1809,11 @@ namespace Avalonia.Controls.UnitTests
 
         private class ClipboardStub : IClipboard // in order to get tests working that use the clipboard
         {
-            private string _text;
+            private string? _text;
 
-            public Task<string> GetTextAsync() => Task.FromResult(_text);
+            public Task<string?> GetTextAsync() => Task.FromResult(_text);
 
-            public Task SetTextAsync(string text)
+            public Task SetTextAsync(string? text)
             {
                 _text = text;
                 return Task.CompletedTask;
@@ -1817,14 +1829,14 @@ namespace Avalonia.Controls.UnitTests
 
             public Task<string[]> GetFormatsAsync() => Task.FromResult(Array.Empty<string>());
 
-            public Task<object> GetDataAsync(string format) => Task.FromResult((object)null);
+            public Task<object?> GetDataAsync(string format) => Task.FromResult((object?)null);
         }
 
         private class TestTopLevel : TopLevel
         {
             private readonly ILayoutManager _layoutManager;
 
-            public TestTopLevel(ITopLevelImpl impl, ILayoutManager layoutManager = null)
+            public TestTopLevel(ITopLevelImpl impl, ILayoutManager? layoutManager = null)
                 : base(impl)
             {
                 _layoutManager = layoutManager ?? new LayoutManager(this);

tests/Avalonia.Controls.UnitTests/WindowTests.cs

@@ -1072,7 +1072,7 @@ namespace Avalonia.Controls.UnitTests
                     var task = target.ShowDialog<bool>(parent);
 
                     target.IsVisible = false;
-                    
+
                     Assert.True(task.IsCompletedSuccessfully);
                 }
             }

tests/Avalonia.DesignerSupport.Tests/RemoteProtocolTests.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Net;
 using System.Net.Sockets;
@@ -80,6 +81,7 @@ namespace Avalonia.DesignerSupport.Tests
         }
         
         [Fact]
+        [SuppressMessage("Usage", "xUnit1031:Do not use blocking task operations in test method", Justification = "Sync context is explicitly disabled")]
         void EntitiesAreProperlySerializedAndDeserialized()
         {
             Init();

tests/Avalonia.Generators.Tests/XamlXNameResolverTests.cs

@@ -22,9 +22,9 @@ public class XamlXNameResolverTests
         var controls = ResolveNames(xaml);
 
         Assert.NotEmpty(controls);
-        Assert.Equal(1, controls.Count);
-        Assert.Equal("UserNameTextBox", controls[0].Name);
-        Assert.Contains(typeof(TextBox).FullName!, controls[0].TypeName);
+        var control = Assert.Single(controls);
+        Assert.Equal("UserNameTextBox", control.Name);
+        Assert.Contains(typeof(TextBox).FullName!, control.TypeName);
     }
 
     [Theory]

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

@@ -244,7 +244,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 
                 window.DataContext = dataContext;
 
-                Assert.Equal(dataContext.TaskProperty.Result, textBlock.Text);
+                Assert.Equal("foobar", textBlock.Text);
             }
         }
 
@@ -1920,7 +1920,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
         [Theory]
         [InlineData(null, "Not called")]
         [InlineData("A", "Do A")]
-        public void Binding_Method_With_Parameter_To_Command_CanExecute(object commandParameter, string result)
+        public void Binding_Method_With_Parameter_To_Command_CanExecute(object? commandParameter, string result)
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {

tests/Avalonia.RenderTests/TestBase.cs

@@ -99,7 +99,7 @@ namespace Avalonia.Direct2D1.RenderTests
                     var immediateError = TestRenderHelper.CompareImages(immediate!, expected);
                     if (immediateError > AllowedError)
                     {
-                        Assert.True(false, immediatePath + ": Error = " + immediateError);
+                        Assert.Fail(immediatePath + ": Error = " + immediateError);
                     }
                 }
 
@@ -108,7 +108,7 @@ namespace Avalonia.Direct2D1.RenderTests
                     var compositedError = TestRenderHelper.CompareImages(composited!, expected);
                     if (compositedError > AllowedError)
                     {
-                        Assert.True(false, compositedPath + ": Error = " + compositedError);
+                        Assert.Fail(compositedPath + ": Error = " + compositedError);
                     }
                 }
             }

tests/Avalonia.RenderTests/TestRenderHelper.cs

@@ -172,7 +172,7 @@ static class TestRenderHelper
 
             if (immediateError > 0.022)
             {
-                Assert.True(false, actualPath + ": Error = " + immediateError);
+                Assert.Fail(actualPath + ": Error = " + immediateError);
             }
         }
     }

tests/Avalonia.Skia.UnitTests/Media/EmbeddedFontCollectionTests.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable enable
+
+using System;
 using System.Collections;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
@@ -32,7 +34,7 @@ namespace Avalonia.Skia.UnitTests.Media
 
                 Assert.True(fontCollection.TryGetGlyphTypeface("Noto Mono", fontStyle, fontWeight, FontStretch.Normal, out var glyphTypeface));
 
-                var actual = glyphTypeface?.FamilyName;
+                var actual = glyphTypeface.FamilyName;
 
                 Assert.Equal("Noto Mono", actual);
             }
@@ -49,7 +51,7 @@ namespace Avalonia.Skia.UnitTests.Media
 
                 fontCollection.Initialize(new CustomFontManagerImpl());
 
-                Assert.False(fontCollection.TryGetGlyphTypeface("ABC", FontStyle.Normal, FontWeight.Normal, FontStretch.Normal, out var glyphTypeface));
+                Assert.False(fontCollection.TryGetGlyphTypeface("ABC", FontStyle.Normal, FontWeight.Normal, FontStretch.Normal, out _));
             }
         }
 

tests/Avalonia.Skia.UnitTests/Media/FontCollectionTests.cs

@@ -1,4 +1,6 @@
-using System.Collections.Concurrent;
+#nullable enable
+
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using Avalonia.Media;
 using Avalonia.Media.Fonts;
@@ -41,7 +43,7 @@ namespace Avalonia.Skia.UnitTests.Media
 
                 Assert.True(glyphTypeface.FontSimulations == FontSimulations.Bold);
 
-                Assert.True(fontCollection.GlyphTypfaceCache.TryGetValue("Arial", out var glyphTypefaces));
+                Assert.True(fontCollection.GlyphTypefaceCache.TryGetValue("Arial", out var glyphTypefaces));
 
                 Assert.Equal(2, glyphTypefaces.Count);
 
@@ -60,7 +62,7 @@ namespace Avalonia.Skia.UnitTests.Media
                 
             }
 
-            public IDictionary<string, ConcurrentDictionary<FontCollectionKey, IGlyphTypeface?>> GlyphTypfaceCache => _glyphTypefaceCache;
+            public IDictionary<string, ConcurrentDictionary<FontCollectionKey, IGlyphTypeface?>> GlyphTypefaceCache => _glyphTypefaceCache;
         }
     }
 }