These two pending tests were added in a56a4cc2. Maybe @BDQ has an idea of where to go in this case? 

It doesn't make sense to me to even have this check here because it iterates through `shipment_units`, removing as many as quantity specifies. So if there are 3 shipment_units, but quantity is 4, I can't see a situation where it would attempt to remove more than those 3. It seems impossible. Do you understand?