MsBuild file to run multiple test projects through mstest and put results into a single file

RunAllTests.proj

<Project ToolsVersion="4.0" DefaultTarget="RunTests" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

  <PropertyGroup>
    <results_file>./TestResults/results.trx</results_file>
  </PropertyGroup>

  <PropertyGroup>
    <MsTestExePath Condition="'$(MsTestExePath)'==''">C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\MSTest.exe</MsTestExePath>
  </PropertyGroup>

  <ItemGroup>
    <TestAssemblies Include=".\**\bin\**\*.Tests.dll" />
  </ItemGroup>

  <ItemGroup>
    <ResultsFile Include="$(results_file)" />
  </ItemGroup>

  <Target Name="RunTests">
    <Message Text="Found test assemblies: @(TestAssemblies)" />

    <MakeDir Directories="./TestResults" />
    <CallTarget Targets="RunMsTest" />
  </Target>

  <Target Name="RunMsTest" >
    <Message Text="Running to results file: %(ResultsFile.Identity)" />

    <PropertyGroup>
      <MsTestCommand>"$(MsTestExePath)" @(TestAssemblies ->'/testcontainer:&quot;%(RecursiveDir)%(Filename)%(Extension)&quot; ', ' ') /resultsfile:TestResults\%(ResultsFile.Identity)</MsTestCommand>
    </PropertyGroup>

    <Message Text="Running command $(MsTestCommand)" />

    <Exec Condition=" '@(TestAssemblies)' != ''" Command="$(MsTestCommand)" ContinueOnError="true">
      <Output TaskParameter="ExitCode" ItemName="ErrorCode"/>
    </Exec>
    <Message Text="Tests complete" />
    <Message Text="The exit code is $(ErrorCode)"/>
    <Error Text="Error while executing MSTest" Condition="'$(ErrorCode)' != ''" />
    <OnError ExecuteTargets="MessageErrorHandler"/>       
  </Target>

  <Target Name="MessageErrorHandler">
    <Message Text="An error has occurred while executing MSTest"/>
  </Target>

</Project>