public void ProcessBuilderDownloadCompleted_NotNullException_ShowsPopup() { //Arrange var popupMock = PopupMock.Create().NotifyFailureMustBeCalled(Arg.IsAny<Exception>()); var vm = new MainViewModel {ThePopupFactory = popupMock.ThePopupFactory}; //Act vm.ProcessBuilderDownloadCompleted(new Exception()); //Assert popupMock.AssertNotifyFailureCalled(); }