Using FactoryGirl.Net with MSTest http://codebetter.com/jameskovacs/2012/03/20/building-factorygirl-net/

FactoryGirlSetup.cs

[TestClass]
public static class Initializer
{
    [AssemblyInitialize]
    public static void InitFactories(TestContext context)
    {
        var factoryTypes = Assembly.GetExecutingAssembly()
            .GetTypes().Where(x => x.Name.EndsWith("Factory"))
            .ToList();

        FactoryGirl.ClearFactoryDefinitions();
        foreach (var factoryType in factoryTypes)
        {
            factoryType.GetMethod("Init").Invoke(null, new object[]{});
        }
    }
}

public static class UserFactory
{
    public static void Init()
    {
        FactoryGirl.Define(() =>
            new User
            {
                Id          = Guid.NewGuid(),
                FirstName   = "Test",
                LastName    = "User",
                Email       = "email@address.com",
                Password    = MongoMembershipProvider.GetMD5Hash("p@ssw0rd")
            });
    }
}