[ADD] stock: test on inventory and duplicated quants
[ADD] stock: test on inventory and duplicated quants

This is not linked to an issue. I thought there was one so i made the
test but actually it's working as expected, so let's commit the test.

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo