add test case & amend error check

pallet/marketplace/src/impls.rs

@@ -312,7 +312,7 @@ impl<T: Config> Pallet<T> {
 	) -> Result<OfferId, DispatchError> {
 		ensure!(!amount.is_zero(), Error::<T>::ZeroOffer);
 		let token_owner = T::NFTExt::get_token_owner(&token_id);
-		ensure!(!token_owner.is_none(), Error::<T>::NoTokenOwner);
+		ensure!(token_owner.is_some(), Error::<T>::NoToken);
 		ensure!(token_owner != Some(who), Error::<T>::IsTokenOwner);
 		let offer_id = Self::next_offer_id();
 		ensure!(offer_id.checked_add(One::one()).is_some(), Error::<T>::NoAvailableIds);

pallet/marketplace/src/lib.rs

@@ -325,8 +325,8 @@ pub mod pallet {
 		TokenOnAuction,
 		/// No tokens were specified in the listing
 		EmptyTokens,
-		/// Token does not have an owner, likely the token has been burnt
-		NoTokenOwner,
+		/// The token does not exist
+		NoToken,
 	}
 
 	#[pallet::hooks]

pallet/marketplace/src/tests.rs

@@ -2191,7 +2191,27 @@ fn make_simple_offer_on_burnt_token_should_fail() {
 				NativeAssetId::get(),
 				None
 			),
-			Error::<Test>::NoTokenOwner
+			Error::<Test>::NoToken
+		);
+	});
+}
+
+#[test]
+fn make_simple_offer_on_non_existent_token_should_fail() {
+	let buyer = create_account(7);
+
+	TestExt::<Test>::default().build().execute_with(|| {
+		let (collection_id, _, _) = setup_nft_token();
+		let offer_amount: Balance = 100;
+		assert_noop!(
+			Marketplace::make_simple_offer(
+				Some(buyer).into(),
+				(collection_id, 456), // non existent token
+				offer_amount,
+				NativeAssetId::get(),
+				None
+			),
+			Error::<Test>::NoToken
 		);
 	});
 }