I\'m checking ModelState.IsValid in my controller action method that creates an Employee like this:
[HttpPost]
public virtual ActionResult Crea
You don't need to mock it. If you already have a controller you can add a model state error when initializing your test:
// arrange
_controllerUnderTest.ModelState.AddModelError("key", "error message");
// act
// Now call the controller action and it will
// enter the (!ModelState.IsValid) condition
var actual = _controllerUnderTest.Index();