unittest ActionFilterAttribute OnActionExecutingAsync with moq

I'm trying to write a unittets for an asp.net webapi project. What I want to do is, to test a function with its corresponding filter. I setup the controller and the filter moq objects like this:

var filtermock= new Mock<MyActionFilterAttribute>();
filtermock.SetupGet(attr => attr.UserId).Returns(userName);
[...]
var controllermock = new Mock<MyController>();
var filtermock = new Mock<MyActionFilterAttribute>();

The unittest looks like this:

var controller = controllermock.Object;
var filter = filtermock.Object;
await filter.OnActionExecutingAsync(null, CancellationToken.None);
await controller.MyTestFunction();
await filter.OnActionExecutedAsync(null, CancellationToken.None);

The problem is, that the overridden functions OnActionExecutingAsync and OnActionExecudedAsync are not beeing called when i run/debug the test. I guess the baseclasses of ActionFilterAttribute are called? Could anyone give me a hint what I am doing wrong here?