ViewData.Model is always null on Unit Test

on my controller

public ViewResult HelloWorld()
{
    List<Sample> testData = new List<Sample>();
    return View(testData);
}

on my unit test

[TestMethod]
public void TestMethod1()
{
    var controller = new AdminController();
    var result = (ViewResult)controller.HelloWorld();
    List<Sample> testData = (List<Sample>)result.ViewData.Model;
}

when debugging, I always see there is something on testData on the quickwatch. but is always ends up as null when not on the quickwatch.