Improve speed of VS test runs

- related to aspnet#11 (4 of 4 additions)
- need xUnit.net AppDomain support in console runs but not in VS runs
 - setting in `WebStack.xunit.targets` overrides `xunit.runner.json` default
 - somewhat avoids issues such as xunit/xunit#353 and xunit/xunit#947
- pre-enumerating `[Theory]`s also slows down test discovery and execution
 - remains a good idea to leave the test execution engine running

Author: dougbu

test/Microsoft.TestCommon/Microsoft.TestCommon.csproj

@@ -107,6 +107,14 @@
   </ItemGroup>
   <ItemGroup>
     <None Include="packages.config" />
+    <None Include="xunit.runner.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <ProjectExtensions>
+    <VisualStudio>
+      <UserProperties xunit_1runner_1json__JSONSchema="https://xunit.github.io/schema/v2.1-rc1/xunit.runner.schema.json" />
+    </VisualStudio>
+  </ProjectExtensions>
 </Project>

test/Microsoft.TestCommon/xunit.runner.json

@@ -0,0 +1,4 @@
+{
+  "appDomain": "denied",
+  "preEnumerateTheories": false
+}

tools/WebStack.xunit.targets

@@ -9,7 +9,8 @@
     <UsingTask TaskName="Xunit.Runner.MSBuild.xunit" AssemblyFile="@(XunitMsBuildRunner)"/>
 
     <Target Name="Xunit">
-        <xunit Assemblies="$(TestAssembly)" XmlV1="$(XmlPath)"/>
+        <!-- Override AppDomains default (set in xunit.runner.json). Need them with this runner. -->
+        <xunit AppDomains="true" Assemblies="$(TestAssembly)" XmlV1="$(XmlPath)"/>
         <!-- Replace potentially illegal escaped characters (if they get through validations done during Save) -->
         <RegexReplace
             Files="$(XmlPath)"