Merge pull request #330 from xiaomi7732/dev/saars/bump-up-testhost

Bump up unit test sdk to 17.4.0

tests/UnitTests/UnitTests.csproj

@@ -10,7 +10,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.5.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.4.0" />
     <PackageReference Include="Moq" Version="4.*" />
     <PackageReference Include="xunit" Version="2.4.*" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.*" />