How can I use a separate AppDomain for each xUnit.net test method?

Question

xUnit uses the same AppDomain for the whole test assembly, this is problematic as I'm testing a UI library and need to create a new Application instance for each individual test.

It works when I run a single test, but when I Run All the first test passed, but all subsequent tests fail with Cannot create more than one System.Windows.Application instance in the same AppDomain at the line where I create a new Application object.

Answer 1

Perhaps you could try by making your test class like this:

public class DomainIsolatedTests : IDisposable
{
  private static int index = 0;
  private readonly AppDomain testDomain;

  public DomainIsolatedTests()
  {
    var name= string.Concat("TestDomain #", ++index);
    testDomain = AppDomain.CreateDomain(name, AppDomain.CurrentDomain.Evidence, AppDomain.CurrentDomain.SetupInformation);
    // Trace.WriteLine(string.Format("[{0}] Created.", testDomain.FriendlyName)); 
  }

  public void Dispose()
  {
    if (testDomain != null)
    {        
      // Trace.WriteLine(string.Format("[{0}] Unloading.", testDomain.FriendlyName));
      AppDomain.Unload(testDomain);        
    }
  }

  [Fact]
  public void Test1()
  {
    testDomain.DoCallBack(() => {
      var app = new System.Windows.Application();

      ...
      // assert
    });
  }

  [Fact]
  public void Test2()
  {
    testDomain.DoCallBack(() => { 
      var app = new System.Windows.Application();

      ...
      // assert
    });
  }

  [Fact]
  public void Test3()
  {
    testDomain.DoCallBack(() => {
      var app = new System.Windows.Application();

      ...
      // assert
    });
  }

  ...
}