How can I run NUnit tests in parallel?

If you want to run NUnit tests in parallel, there are at least 2 options:

• NCrunch offers it out of the box (without changing anything, but is a commercial product)
• NUnit 3 offers a Parallelizable attribute, which can be used to denote which tests can be run in parallel

NUnit version 3 will support running tests in parallel:

Adding the attribute to a class: [Parallelizable(ParallelScope.Self)] will run your tests in parallel.

• ParallelScope.None indicates that the test may not be run in parallel with other tests.

• ParallelScope.Self indicates that the test itself may be run in parallel with other tests.

• ParallelScope.Children indicates that the descendants of the test may be run in parallel with respect to one another.

• ParallelScope.Fixtures indicates that fixtures may be run in parallel with one another.

NUnit Framework-Parallel-Test-Execution

If your project contains multiple test DLLs you can run them in parallel using this MSBuild script. Obviously you'll need to tweak the paths to suit your project layout.

To run with 8 cores run with: c:\proj> msbuild /m:8 RunTests.xml

RunTests.xml

<?xml version="1.0" encoding="utf-8"?>
<Project DefaultTargets="RunTestsInParallel" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="$(MSBuildExtensionsPath)\MSBuildCommunityTasks\MSBuild.Community.Tasks.Targets"/>
  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Release</Configuration>
    <Nunit Condition=" '$(Nunit)' == '' ">$(MSBuildProjectDirectory)\..\tools\nunit-console-x86.exe</Nunit>
  </PropertyGroup>

  <!-- see http://mikefourie.wordpress.com/2010/12/04/running-targets-in-parallel-in-msbuild/ -->

  <Target Name="RunTestsInParallel">
    <ItemGroup> 
      <TestDlls Include="..\bin\Tests\$(Configuration)\*.Tests.dll" />
    </ItemGroup>

    <ItemGroup> 
      <TempProjects Include="$(MSBuildProjectFile)" > 
        <Properties>TestDllFile=%(TestDlls.FullPath)</Properties> 
      </TempProjects> 
    </ItemGroup> 

    <MSBuild Projects="@(TempProjects)" BuildInParallel="true" Targets="RunOneTestDll" /> 
  </Target>

  <Target Name="RunOneTestDll"> 
    <Message Text="$(TestDllFile)" />
    <Exec Command="$(Nunit) /exclude=Integration $(TestDllFile)  /labels /xml:$(TestDllFile).results.xml"
      WorkingDirectory="$(MSBuildProjectDirectory)\..\bin\Tests\$(Configuration)" /> 
  </Target>

</Project>

Update If I were answering this question now I would highly recommend NCrunch and its command line test running tool for maximum test run performance. There's nothing like it and it'll revolutionise your code-test-debug cycle at the same time.

As an alternative to adding the Parallelizable attribute to every test class:

Add this into the test project AssemblyInfo.cs class for nunit3 or greater:

// Make all tests in the test assembly run in parallel
[assembly: Parallelizable(ParallelScope.Fixtures)]