chore: add code coverage

tests/Directory.Build.props

@@ -1,3 +1,9 @@
 <Project>
-  <Import Project="$([MSBuild]::GetPathOfFileAbove('Directory.Build.props', '$(MSBuildThisFileDirectory)../'))" />
+  <Import
+    Project="$([MSBuild]::GetPathOfFileAbove('Directory.Build.props', '$(MSBuildThisFileDirectory)../'))" />
+
+  <PropertyGroup>
+    <TestingPlatformDotnetTestSupport>true</TestingPlatformDotnetTestSupport>
+    <TestingPlatformCommandLineArguments>--coverage --coverage-output-format cobertura</TestingPlatformCommandLineArguments>
+  </PropertyGroup>
 </Project>