Extended the add test a bit.
Don't allow the same person to be on the same item twice. Prevent this by adding a uniqueness constraint to the ItemPerson model.
Added a test for this as well. This, at least, should prevent the problem that Michael Abbott had with ProgDB allowing multiple additions of the same person, but removing all of them when you tried to remove one.
More testing, for removing people from items.
Extending a bit more.