public void RetrieveTicketScan_IdentifierNull_ThrowsArgumentNullException()
{
// Arrange
var identifier = (string)null;
// Act
var retrieveTicketScanCall = new Action(() => _detailsViewModel.RetrieveTicketScan(identifier));
// Assert
Assert.That(retrieveTicketScanCall, Throws.Exception.TypeOf <ArgumentNullException>());
}