Running NUnit tests on .NET 4 assemblies with MSBuild

If you want to run NUnit tests with MSBuild, then you need to download and install the MSBuild Community tasks. This allows you to create a unit test target like this:

<ItemGroup>
  <TestAssembly Include="ClientBin\*Tests.dll" />
</ItemGroup>
<Target Name="Test" DependsOnTargets="Build">
  <NUnit Assemblies="@(TestAssembly)"
         WorkingDirectory="."
         ToolPath="C:\Program Files\NUnit 2.5.5\bin\net-2.0"
         />
</Target>

(Most examples don’t show the need to specify a ToolPath, but I have found I need it, perhaps because it isn’t in my Path?)

The trouble is, if the assemblies containing the unit tests have been build with the .NET 4 framework, you will get the following error:

C:\Program Files\NUnit 2.5.5\bin\net-2.0\nunit-console.exe /nologo ClientBin\
Nice.Inform.Client.Tests.dll
ProcessModel: Default    DomainUsage: Single
Execution Runtime: net-2.0
Unhandled Exception:
System.BadImageFormatException: Could not load file or assembly 'D:\TFS\Trial
\Inform5\ClientBin\Client.Tests.dll' or one of its dependencies.
This assembly is built by a runtime newer than the currently loaded runtime a
nd cannot be loaded.
File name: 'D:\TFS\Trial\Inform5\ClientBin\Client.Tests.dll'

What is needed is to ensure that nunit-console.exe runs against the .NET 4 framework. The way I achieved this was to make a copy of the net-2.0 folder that comes with NUnit 2.5.5 and rename it to net-4.0 (n.b. make sure the lib folder comes along too as nunit-console.exe depends on its contents). Then, I edited the nunit-console.exe.config file to have the following contents (the key bit is to add the supportedRuntime setting):

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <!-- Set the level for tracing NUnit itself -->
  <!-- 0=Off 1=Error 2=Warning 3=Info 4=Debug -->
  <system.diagnostics>
    <switches>
       <add name="NTrace" value="0" />
    </switches>
  </system.diagnostics>

  <startup>
    <supportedRuntime version="v4.0"/>
  </startup>

  <runtime>
    <!-- We need this so test exceptions don't crash NUnit -->
    <legacyUnhandledExceptionPolicy enabled="1" />

    <!-- Look for addins in the addins directory for now -->
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <probing privatePath="lib;addins"/>
   </assemblyBinding>
  </runtime>
</configuration>

Now all that is needed is to update the ToolPath in the MSBuild script to point to the new location

<Target Name="Test" DependsOnTargets="Build">
  <NUnit Assemblies="@(TestAssembly)"
        WorkingDirectory="."
        ToolPath="C:\Program Files\NUnit 2.5.5\bin\net-4.0"
   />
</Target>

I’d be interested in hearing if there is an easier way of solving this problem though, as I don’t really want to have to require all developers to manually perform these steps on their machine.