public void CustomerController_ChangeOwner_Exception_AppendsErrorMessageToHeader() { _mockCustomerService.Setup(s => s.GetById(It.IsAny <int>())).Throws(new ApplicationException("Oh no!!")); _controllerWithMockedCustomerService.ChangeOwner(new ChangeCustomerOwnerViewModel()); _mockResponseManager.Verify(v => v.AppendHeader(ModelStateErrorNames.ErrorMessage, It.IsAny <string>()), Times.Once); }