Preparation for the new test runner (#1174)

Context: https://github.com/xamarin/xamarin-android/pull/1075

PR #1075 keeps rebuilding all the Mono runtimes because of the
`build-tools/mono-runtimes/*` changes -- which invalidate the bundle
hash (97f08f78) -- which means the entire world needs to be rebuilt,
which is *very slow* (7+ hours per build).

This is getting quite tiresome.

Split out the `build-tools/mono-runtimes` changes from PR #1075
so that a new bundle can be built *and cached*, which will speed
up subsequent PR #1075 builds.

build-tools/mono-runtimes/ProfileAssemblies.projitems

@@ -192,6 +192,10 @@
     <MonoTestAssembly Include="monodroid_corlib_test.dll">
       <SourcePath>corlib</SourcePath>
     </MonoTestAssembly>
+    <MonoTestAssembly Include="monodroid_corlib_xunit-test.dll">
+      <SourcePath>corlib</SourcePath>
+      <TestType>xunit</TestType>
+    </MonoTestAssembly>
     <MonoTestAssembly Include="monodroid_I18N.CJK_test.dll">
       <SourcePath>I18N/CJK</SourcePath>
     </MonoTestAssembly>
@@ -237,6 +241,10 @@
     <MonoTestAssembly Include="monodroid_System.Numerics_test.dll">
       <SourcePath>System.Numerics</SourcePath>
     </MonoTestAssembly>
+    <MonoTestAssembly Include="monodroid_System.Numerics_xunit-test.dll">
+      <SourcePath>System.Numerics</SourcePath>
+      <TestType>xunit</TestType>
+    </MonoTestAssembly>
     <MonoTestAssembly Include="monodroid_System.Runtime.Serialization_test.dll">
       <SourcePath>System.Runtime.Serialization</SourcePath>
     </MonoTestAssembly>

build-tools/mono-runtimes/mono-runtimes.targets

@@ -310,6 +310,11 @@
         IgnoreStandardErrorWarningFormat="True"
         WorkingDirectory="$(IntermediateOutputPath)\%(_MonoRuntime.Identity)\runtime"
     />
+    <Exec
+        Condition=" '%(MonoTestAssembly.TestType)' == 'xunit' "
+        Command="make -C $(MonoSourceFullPath)\mcs\class\%(MonoTestAssembly.SourcePath) xunit-test-local"
+        WorkingDirectory="$(MonoSourceFullPath)"
+    />
     <Copy
         SourceFiles="@(_BclTestAssemblySource)"
         DestinationFiles="@(_BclTestAssemblyDestination)"

tests/Xamarin.Android.Bcl-Tests/Xamarin.Android.Bcl-Tests.targets

@@ -5,20 +5,29 @@
   <Import Project="Xamarin.Android.Bcl-Tests.projitems" />
   <Import Project="..\..\build-tools\scripts\TestApks.targets" />
   <Import Project="..\..\build-tools\mono-runtimes\ProfileAssemblies.projitems" />
+  <Target Name="_GetNUnitAssemblies">
+    <ItemGroup>
+      <_NUnitAssembly
+          Condition=" '%(MonoTestAssembly.TestType)' != 'xunit' "
+          Include="@(MonoTestAssembly)"
+      />
+    </ItemGroup>
+  </Target>
   <Target Name="_AddTestAssemblies"
       DependsOnTargets="_RemapAssemblies"
       BeforeTargets="ResolveAssemblyReferences">
     <ItemGroup>
-      <Reference Include="@(MonoTestAssembly->'$(IntermediateOutputPath)%(Identity)')" />
+      <Reference Include="@(_NUnitAssembly->'$(IntermediateOutputPath)%(Identity)')" />
       <Reference Remove="$(IntermediateOutputPath)nunitlite.dll" />
     </ItemGroup>
   </Target>
   <Target Name="_RemapAssemblies"
-      Inputs="@(MonoTestAssembly->'..\..\bin\$(Configuration)\bcl-tests\%(Identity)')"
-      Outputs="@(MonoTestAssembly->'$(IntermediateOutputPath)%(Identity)')">
+      DependsOnTargets="_GetNUnitAssemblies"
+      Inputs="@(_NUnitAssembly->'..\..\bin\$(Configuration)\bcl-tests\%(Identity)')"
+      Outputs="@(_NUnitAssembly->'$(IntermediateOutputPath)%(Identity)')">
     <MakeDir Directories="$(IntermediateOutputPath)" />
     <ItemGroup>
-      <_Source  Include="@(MonoTestAssembly->'..\..\bin\$(Configuration)\bcl-tests\%(Identity)')" />
+      <_Source  Include="@(_NUnitAssembly->'..\..\bin\$(Configuration)\bcl-tests\%(Identity)')" />
     </ItemGroup>
     <ResolveAssemblyReference
         Assemblies="Xamarin.Android.NUnitLite"
@@ -67,11 +76,12 @@
     <Touch Files="@(_TestResource)" />
   </Target>
   <Target Name="_GenerateApp_cs"
-      Inputs="@(MonoTestAssembly->'..\..\bin\$(Configuration)\bcl-tests\%(Identity)')"
+      DependsOnTargets="_GetNUnitAssemblies"
+      Inputs="@(_NUnitAssembly->'..\..\bin\$(Configuration)\bcl-tests\%(Identity)')"
       Outputs="$(IntermediateOutputPath)\App.cs">
     <MakeDir Directories="$(IntermediateOutputPath)" />
     <PropertyGroup>
-      <_Assemblies>@(MonoTestAssembly->'"%(Identity)"', ',  ')</_Assemblies>
+      <_Assemblies>@(_NUnitAssembly->'"%(Identity)"', ',  ')</_Assemblies>
     </PropertyGroup>
     <ReplaceFileContents
         SourceFile="App.cs.in"