What is the proper syntax to use when trying to implement the SetUpFixture ability in Nunit. This is what I have but I keep getting an error: 

```
namespace Testing
{
    [SetUpFixture, RequiresSTA]
    public class SetupClass
    {
        public IE CASsite = new IE("awebsite");

        [SetUp]
        public void Setup()
        {

        }

        [TearDown]
        public void TearDown()
        {
            CASsite.Dispose();
        }

    }

    [TestFixture, RequiresSTA]
    public class Tests : SetupClass
    {
        [Test]
        public void DoSomething()
        {

         }
    }
}

```

The error I keep receiving is : **Failure: TestFixtureSetUp failed in SetupClass**