added coupon related test to the listingInner model unit test
added coupon related test to the listingInner model unit test

jashot7/openbazaar-desktop,srhoulam/openbazaar-desktop,jashot7/openbazaar-desktop,jjeffryes/openbazaar-desktop,jashot7/openbazaar-desktop,OpenBazaar/openbazaar-desktop,srhoulam/openbazaar-desktop,jjeffryes/openbazaar-desktop,OpenBazaar/openbazaar-desktop,OpenBazaar/openbazaar-desktop,jjeffryes/openbazaar-desktop,srhoulam/openbazaar-desktop