Add first test case for ProductSet
Add first test case for ProductSet

This covers creation and update of a product.

Matt-Yorkley/openfoodnetwork,mkllnk/openfoodnetwork,Matt-Yorkley/openfoodnetwork,Matt-Yorkley/openfoodnetwork,mkllnk/openfoodnetwork,mkllnk/openfoodnetwork,mkllnk/openfoodnetwork,openfoodfoundation/openfoodnetwork,lin-d-hop/openfoodnetwork,openfoodfoundation/openfoodnetwork,lin-d-hop/openfoodnetwork,openfoodfoundation/openfoodnetwork,lin-d-hop/openfoodnetwork,openfoodfoundation/openfoodnetwork,lin-d-hop/openfoodnetwork,Matt-Yorkley/openfoodnetwork