Using WPF components in NUnit tests - how to use STA?

Question

I need to use some WPF components in an NUnit unit test. I run the test through ReSharper, and it fails with the following error when using the WPF object:

System.InvalidOperationException:

The calling thread must be STA, because many UI components require this.

I've read about this problem, and it sounds like the thread needs to be STA, but I haven't figured out how to do this yet. What triggers the problem is the following code:

[Test] public void MyTest() {     var textBox = new TextBox();      textBox.Text = "Some text"; // <-- This causes the exception. } 

Answer 1

You should add the RequiresSTA attribut to your test class.

[TestFixture, RequiresSTA] public class MyTestClass { } 

Answer 2

With more recent versions, the attribute has changed :

[Apartment(ApartmentState.STA)] public class MyTestClass {}