Skip WPF test in CI, it fails on releases

Author: kzu

src/System.Diagnostics.Tracer.Tests/System.Diagnostics.Tracer.Tests.csproj

@@ -9,9 +9,11 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.4.1" />
     <PackageReference Include="Microsoft.TestPlatform.ObjectModel" Version="17.4.1" />
     <PackageReference Include="Moq" Version="4.18.4" />
+    <PackageReference Include="ThisAssembly.Project" Version="1.2.1" />
     <PackageReference Include="xunit" Version="2.4.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5" />
     <PackageReference Include="coverlet.collector" Version="3.2.0" />
+    <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
   </ItemGroup>
 
   <ItemGroup>
@@ -20,6 +22,7 @@
 
   <ItemGroup>
     <Reference Include="WindowsBase" />
+    <ProjectProperty Include="CI" />
   </ItemGroup>
 
 </Project>

src/System.Diagnostics.Tracer.Tests/TracerManagerTests.cs

@@ -6,9 +6,12 @@ namespace System.Diagnostics
 {
     public class TracerManagerTests
     {
-        [Fact]
+        [SkippableFact]
         public void when_getting_source_then_can_retrieve_built_in_source()
         {
+            var ci = bool.TryParse(ThisAssembly.Project.CI, out var value) && value;
+            Skip.If(ci);
+            
             var manager = new TracerManager();
             var expected = PresentationTraceSources.MarkupSource;
             var actual = manager.GetSource("System.Windows.Markup");