XCM WeightTrader: Swap Fee Asset for Native Asset (#1845)

Implements an XCM executor `WeightTrader`, facilitating fee payments in
any asset that can be exchanged for a native asset.

A few constraints need to be observed:
- `buy_weight` and `refund` operations must be atomic, as another weight
trader implementation might be attempted in case of failure.
- swap credit must be utilized since there isn’t an account to which an
asset of some class can be deposited with a guarantee to meet the
existential deposit requirement. Also, operating with credits enhances
the efficiency of the weight trader -
https://github.com/paritytech/polkadot-sdk/pull/1677

related PRs:
- (depends) https://github.com/paritytech/polkadot-sdk/pull/2031
- (depends) https://github.com/paritytech/polkadot-sdk/pull/1677
- (caused) https://github.com/paritytech/polkadot-sdk/pull/1847
- (caused) https://github.com/paritytech/polkadot-sdk/pull/1876

// DONE: impl `OnUnbalanced` for a `fungible/s` credit
// DONE: make the trader free from a concept of a native currency and
drop few fallible conversions. related issue -
https://github.com/paritytech/polkadot-sdk/issues/1842
// DONE: tests

---------

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>

cumulus/parachains/runtimes/assets/asset-hub-westend/src/lib.rs

@@ -295,7 +295,7 @@ impl pallet_assets::Config<PoolAssetsInstance> for Runtime {
 	type BenchmarkHelper = ();
 }
 
-/// Union fungibles implementation for `Assets`` and `ForeignAssets`.
+/// Union fungibles implementation for `Assets` and `ForeignAssets`.
 pub type LocalAndForeignAssets = fungibles::UnionOf<
 	Assets,
 	ForeignAssets,
@@ -307,18 +307,21 @@ pub type LocalAndForeignAssets = fungibles::UnionOf<
 	AccountId,
 >;
 
+/// Union fungibles implementation for [`LocalAndForeignAssets`] and `Balances`.
+pub type NativeAndAssets = fungible::UnionOf<
+	Balances,
+	LocalAndForeignAssets,
+	TargetFromLeft<WestendLocation>,
+	MultiLocation,
+	AccountId,
+>;
+
 impl pallet_asset_conversion::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
 	type Balance = Balance;
 	type HigherPrecisionBalance = sp_core::U256;
 	type AssetKind = MultiLocation;
-	type Assets = fungible::UnionOf<
-		Balances,
-		LocalAndForeignAssets,
-		TargetFromLeft<WestendLocation>,
-		Self::AssetKind,
-		Self::AccountId,
-	>;
+	type Assets = NativeAndAssets;
 	type PoolId = (Self::AssetKind, Self::AssetKind);
 	type PoolLocator =
 		pallet_asset_conversion::WithFirstAsset<WestendLocation, AccountId, Self::AssetKind>;

cumulus/parachains/runtimes/assets/asset-hub-westend/src/xcm_config.rs

@@ -15,17 +15,21 @@
 
 use super::{
 	AccountId, AllPalletsWithSystem, Assets, Authorship, Balance, Balances, BaseDeliveryFee,
-	FeeAssetId, ForeignAssets, ForeignAssetsInstance, ParachainInfo, ParachainSystem, PolkadotXcm,
-	PoolAssets, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin, ToRococoXcmRouter,
-	TransactionByteFee, TrustBackedAssetsInstance, WeightToFee, XcmpQueue,
+	CollatorSelection, FeeAssetId, ForeignAssets, ForeignAssetsInstance, ParachainInfo,
+	ParachainSystem, PolkadotXcm, PoolAssets, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin,
+	ToRococoXcmRouter, TransactionByteFee, TrustBackedAssetsInstance, WeightToFee, XcmpQueue,
 };
 use assets_common::{
 	local_and_foreign_assets::MatchesLocalAndForeignAssetsMultiLocation,
 	matching::{FromSiblingParachain, IsForeignConcreteAsset},
+	TrustBackedAssetsAsMultiLocation,
 };
 use frame_support::{
 	match_types, parameter_types,
-	traits::{ConstU32, Contains, Equals, Everything, Nothing, PalletInfoAccess},
+	traits::{
+		tokens::imbalance::ResolveAssetTo, ConstU32, Contains, Equals, Everything, Nothing,
+		PalletInfoAccess,
+	},
 };
 use frame_system::EnsureRoot;
 use pallet_xcm::XcmPassthrough;
@@ -70,6 +74,7 @@ parameter_types! {
 	pub PoolAssetsPalletLocation: MultiLocation =
 		PalletInstance(<PoolAssets as PalletInfoAccess>::index() as u8).into();
 	pub CheckingAccount: AccountId = PolkadotXcm::check_account();
+	pub StakingPot: AccountId = CollatorSelection::account_id();
 	pub TreasuryAccount: AccountId = TREASURY_PALLET_ID.into_account_truncating();
 	pub RelayTreasuryLocation: MultiLocation = (Parent, PalletInstance(westend_runtime_constants::TREASURY_PALLET_ID)).into();
 }
@@ -567,31 +572,17 @@ impl xcm_executor::Config for XcmConfig {
 	>;
 	type Trader = (
 		UsingComponents<WeightToFee, WestendLocation, AccountId, Balances, ToStakingPot<Runtime>>,
-		// This trader allows to pay with `is_sufficient=true` "Trust Backed" assets from dedicated
-		// `pallet_assets` instance - `Assets`.
-		cumulus_primitives_utility::TakeFirstAssetTrader<
+		cumulus_primitives_utility::SwapFirstAssetTrader<
+			WestendLocation,
+			crate::AssetConversion,
+			WeightToFee,
+			crate::NativeAndAssets,
+			(
+				TrustBackedAssetsAsMultiLocation<TrustBackedAssetsPalletLocation, Balance>,
+				ForeignAssetsConvertedConcreteId,
+			),
+			ResolveAssetTo<StakingPot, crate::NativeAndAssets>,
 			AccountId,
-			AssetFeeAsExistentialDepositMultiplierFeeCharger,
-			TrustBackedAssetsConvertedConcreteId,
-			Assets,
-			cumulus_primitives_utility::XcmFeesTo32ByteAccount<
-				FungiblesTransactor,
-				AccountId,
-				XcmAssetFeesReceiver,
-			>,
-		>,
-		// This trader allows to pay with `is_sufficient=true` "Foreign" assets from dedicated
-		// `pallet_assets` instance - `ForeignAssets`.
-		cumulus_primitives_utility::TakeFirstAssetTrader<
-			AccountId,
-			ForeignAssetFeeAsExistentialDepositMultiplierFeeCharger,
-			ForeignAssetsConvertedConcreteId,
-			ForeignAssets,
-			cumulus_primitives_utility::XcmFeesTo32ByteAccount<
-				ForeignFungiblesTransactor,
-				AccountId,
-				XcmAssetFeesReceiver,
-			>,
 		>,
 	);
 	type ResponseHandler = PolkadotXcm;

cumulus/parachains/runtimes/assets/asset-hub-westend/tests/tests.rs

@@ -18,28 +18,36 @@
 //! Tests for the Westmint (Westend Assets Hub) chain.
 
 use asset_hub_westend_runtime::{
+	xcm_config,
 	xcm_config::{
-		self, bridging, AssetFeeAsExistentialDepositMultiplierFeeCharger, CheckingAccount,
-		ForeignCreatorsSovereignAccountOf, LocationToAccountId, TrustBackedAssetsPalletLocation,
-		WestendLocation, XcmConfig,
+		bridging, ForeignCreatorsSovereignAccountOf, LocationToAccountId, WestendLocation,
 	},
-	AllPalletsWithoutSystem, AssetDeposit, Assets, Balances, ExistentialDeposit, ForeignAssets,
-	ForeignAssetsInstance, MetadataDepositBase, MetadataDepositPerByte, ParachainSystem,
-	PolkadotXcm, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin, SessionKeys,
-	ToRococoXcmRouterInstance, TrustBackedAssetsInstance, XcmpQueue,
+	AllPalletsWithoutSystem, MetadataDepositBase, MetadataDepositPerByte, PolkadotXcm, RuntimeCall,
+	RuntimeEvent, RuntimeOrigin, ToRococoXcmRouterInstance, XcmpQueue,
+};
+pub use asset_hub_westend_runtime::{
+	xcm_config::{CheckingAccount, TrustBackedAssetsPalletLocation, XcmConfig},
+	AssetConversion, AssetDeposit, Assets, Balances, CollatorSelection, ExistentialDeposit,
+	ForeignAssets, ForeignAssetsInstance, ParachainSystem, Runtime, SessionKeys, System,
+	TrustBackedAssetsInstance,
 };
 use asset_test_utils::{
 	test_cases_over_bridge::TestBridgingConfig, CollatorSessionKey, CollatorSessionKeys, ExtBuilder,
 };
 use codec::{Decode, Encode};
-use cumulus_primitives_utility::ChargeWeightInFungibles;
 use frame_support::{
-	assert_noop, assert_ok,
-	traits::fungibles::InspectEnumerable,
+	assert_ok,
+	traits::{
+		fungible::{Inspect, Mutate},
+		fungibles::{
+			Create, Inspect as FungiblesInspect, InspectEnumerable, Mutate as FungiblesMutate,
+		},
+	},
 	weights::{Weight, WeightToFee as WeightToFeeT},
 };
 use parachains_common::{
-	westend::fee::WeightToFee, AccountId, AssetIdForTrustBackedAssets, AuraId, Balance,
+	westend::{currency::UNITS, fee::WeightToFee},
+	AccountId, AssetIdForTrustBackedAssets, AuraId, Balance,
 };
 use sp_runtime::traits::MaybeEquivalence;
 use std::convert::Into;
@@ -67,7 +75,7 @@ fn collator_session_keys() -> CollatorSessionKeys<Runtime> {
 }
 
 #[test]
-fn test_asset_xcm_trader() {
+fn test_buy_and_refund_weight_in_native() {
 	ExtBuilder::<Runtime>::default()
 		.with_collators(vec![AccountId::from(ALICE)])
 		.with_session_keys(vec![(
@@ -77,77 +85,55 @@ fn test_asset_xcm_trader() {
 		)])
 		.build()
 		.execute_with(|| {
-			// We need root origin to create a sufficient asset
-			let minimum_asset_balance = 3333333_u128;
-			let local_asset_id = 1;
-			assert_ok!(Assets::force_create(
-				RuntimeHelper::root_origin(),
-				local_asset_id.into(),
-				AccountId::from(ALICE).into(),
-				true,
-				minimum_asset_balance
-			));
+			let bob: AccountId = SOME_ASSET_ADMIN.into();
+			let staking_pot = CollatorSelection::account_id();
+			let native_location = WestendLocation::get();
+			let initial_balance = 200 * UNITS;
 
-			// We first mint enough asset for the account to exist for assets
-			assert_ok!(Assets::mint(
-				RuntimeHelper::origin_of(AccountId::from(ALICE)),
-				local_asset_id.into(),
-				AccountId::from(ALICE).into(),
-				minimum_asset_balance
-			));
+			assert_ok!(Balances::mint_into(&bob, initial_balance));
+			assert_ok!(Balances::mint_into(&staking_pot, initial_balance));
 
-			// get asset id as multilocation
-			let asset_multilocation =
-				AssetIdForTrustBackedAssetsConvert::convert_back(&local_asset_id).unwrap();
+			// keep initial total issuance to assert later.
+			let total_issuance = Balances::total_issuance();
 
-			// Set Alice as block author, who will receive fees
-			RuntimeHelper::run_to_block(2, AccountId::from(ALICE));
-
-			// We are going to buy 4e9 weight
-			let bought = Weight::from_parts(4_000_000_000u64, 0);
-
-			// Lets calculate amount needed
-			let asset_amount_needed =
-				AssetFeeAsExistentialDepositMultiplierFeeCharger::charge_weight_in_fungibles(
-					local_asset_id,
-					bought,
-				)
-				.expect("failed to compute");
-
-			// Lets pay with: asset_amount_needed + asset_amount_extra
-			let asset_amount_extra = 100_u128;
-			let asset: MultiAsset =
-				(asset_multilocation, asset_amount_needed + asset_amount_extra).into();
-
-			let mut trader = <XcmConfig as xcm_executor::Config>::Trader::new();
+			// prepare input to buy weight.
+			let weight = Weight::from_parts(4_000_000_000, 0);
+			let fee = WeightToFee::weight_to_fee(&weight);
+			let extra_amount = 100;
 			let ctx = XcmContext { origin: None, message_id: XcmHash::default(), topic: None };
+			let payment: MultiAsset = (native_location, fee + extra_amount).into();
 
-			// Lets buy_weight and make sure buy_weight does not return an error
-			let unused_assets = trader.buy_weight(bought, asset.into(), &ctx).expect("Expected Ok");
-			// Check whether a correct amount of unused assets is returned
-			assert_ok!(
-				unused_assets.ensure_contains(&(asset_multilocation, asset_amount_extra).into())
-			);
+			// init trader and buy weight.
+			let mut trader = <XcmConfig as xcm_executor::Config>::Trader::new();
+			let unused_asset =
+				trader.buy_weight(weight, payment.into(), &ctx).expect("Expected Ok");
 
-			// Drop trader
+			// assert.
+			let unused_amount =
+				unused_asset.fungible.get(&native_location.into()).map_or(0, |a| *a);
+			assert_eq!(unused_amount, extra_amount);
+			assert_eq!(Balances::total_issuance(), total_issuance);
+
+			// prepare input to refund weight.
+			let refund_weight = Weight::from_parts(1_000_000_000, 0);
+			let refund = WeightToFee::weight_to_fee(&refund_weight);
+
+			// refund.
+			let actual_refund = trader.refund_weight(refund_weight, &ctx).unwrap();
+			assert_eq!(actual_refund, (native_location, refund).into());
+
+			// assert.
+			assert_eq!(Balances::balance(&staking_pot), initial_balance);
+			// only after `trader` is dropped we expect the fee to be resolved into the treasury
+			// account.
 			drop(trader);
-
-			// Make sure author(Alice) has received the amount
-			assert_eq!(
-				Assets::balance(local_asset_id, AccountId::from(ALICE)),
-				minimum_asset_balance + asset_amount_needed
-			);
-
-			// We also need to ensure the total supply increased
-			assert_eq!(
-				Assets::total_supply(local_asset_id),
-				minimum_asset_balance + asset_amount_needed
-			);
-		});
+			assert_eq!(Balances::balance(&staking_pot), initial_balance + fee - refund);
+			assert_eq!(Balances::total_issuance(), total_issuance + fee - refund);
+		})
 }
 
 #[test]
-fn test_asset_xcm_trader_with_refund() {
+fn test_buy_and_refund_weight_with_swap_local_asset_xcm_trader() {
 	ExtBuilder::<Runtime>::default()
 		.with_collators(vec![AccountId::from(ALICE)])
 		.with_session_keys(vec![(
@@ -157,247 +143,192 @@ fn test_asset_xcm_trader_with_refund() {
 		)])
 		.build()
 		.execute_with(|| {
-			// We need root origin to create a sufficient asset
-			// We set existential deposit to be identical to the one for Balances first
-			assert_ok!(Assets::force_create(
-				RuntimeHelper::root_origin(),
-				1.into(),
-				AccountId::from(ALICE).into(),
-				true,
-				ExistentialDeposit::get()
+			let bob: AccountId = SOME_ASSET_ADMIN.into();
+			let staking_pot = CollatorSelection::account_id();
+			let asset_1: u32 = 1;
+			let native_location = WestendLocation::get();
+			let asset_1_location =
+				AssetIdForTrustBackedAssetsConvert::convert_back(&asset_1).unwrap();
+			// bob's initial balance for native and `asset1` assets.
+			let initial_balance = 200 * UNITS;
+			// liquidity for both arms of (native, asset1) pool.
+			let pool_liquidity = 100 * UNITS;
+
+			// init asset, balances and pool.
+			assert_ok!(<Assets as Create<_>>::create(asset_1, bob.clone(), true, 10));
+
+			assert_ok!(Assets::mint_into(asset_1, &bob, initial_balance));
+			assert_ok!(Balances::mint_into(&bob, initial_balance));
+			assert_ok!(Balances::mint_into(&staking_pot, initial_balance));
+
+			assert_ok!(AssetConversion::create_pool(
+				RuntimeHelper::origin_of(bob.clone()),
+				Box::new(native_location),
+				Box::new(asset_1_location)
 			));
 
-			// We first mint enough asset for the account to exist for assets
-			assert_ok!(Assets::mint(
-				RuntimeHelper::origin_of(AccountId::from(ALICE)),
-				1.into(),
-				AccountId::from(ALICE).into(),
-				ExistentialDeposit::get()
+			assert_ok!(AssetConversion::add_liquidity(
+				RuntimeHelper::origin_of(bob.clone()),
+				Box::new(native_location),
+				Box::new(asset_1_location),
+				pool_liquidity,
+				pool_liquidity,
+				1,
+				1,
+				bob,
 			));
 
-			let mut trader = <XcmConfig as xcm_executor::Config>::Trader::new();
+			// keep initial total issuance to assert later.
+			let asset_total_issuance = Assets::total_issuance(asset_1);
+			let native_total_issuance = Balances::total_issuance();
+
+			// prepare input to buy weight.
+			let weight = Weight::from_parts(4_000_000_000, 0);
+			let fee = WeightToFee::weight_to_fee(&weight);
+			let asset_fee =
+				AssetConversion::get_amount_in(&fee, &pool_liquidity, &pool_liquidity).unwrap();
+			let extra_amount = 100;
 			let ctx = XcmContext { origin: None, message_id: XcmHash::default(), topic: None };
+			let payment: MultiAsset = (asset_1_location, asset_fee + extra_amount).into();
 
-			// Set Alice as block author, who will receive fees
-			RuntimeHelper::run_to_block(2, AccountId::from(ALICE));
+			// init trader and buy weight.
+			let mut trader = <XcmConfig as xcm_executor::Config>::Trader::new();
+			let unused_asset =
+				trader.buy_weight(weight, payment.into(), &ctx).expect("Expected Ok");
 
-			// We are going to buy 4e9 weight
-			let bought = Weight::from_parts(4_000_000_000u64, 0);
-			let asset_multilocation = AssetIdForTrustBackedAssetsConvert::convert_back(&1).unwrap();
+			// assert.
+			let unused_amount =
+				unused_asset.fungible.get(&asset_1_location.into()).map_or(0, |a| *a);
+			assert_eq!(unused_amount, extra_amount);
+			assert_eq!(Assets::total_issuance(asset_1), asset_total_issuance + asset_fee);
 
-			// lets calculate amount needed
-			let amount_bought = WeightToFee::weight_to_fee(&bought);
+			// prepare input to refund weight.
+			let refund_weight = Weight::from_parts(1_000_000_000, 0);
+			let refund = WeightToFee::weight_to_fee(&refund_weight);
+			let (reserve1, reserve2) =
+				AssetConversion::get_reserves(native_location, asset_1_location).unwrap();
+			let asset_refund =
+				AssetConversion::get_amount_out(&refund, &reserve1, &reserve2).unwrap();
 
-			let asset: MultiAsset = (asset_multilocation, amount_bought).into();
-
-			// Make sure buy_weight does not return an error
-			assert_ok!(trader.buy_weight(bought, asset.clone().into(), &ctx));
-
-			// Make sure again buy_weight does return an error
-			// This assert relies on the fact, that we use `TakeFirstAssetTrader` in `WeightTrader`
-			// tuple chain, which cannot be called twice
-			assert_noop!(trader.buy_weight(bought, asset.into(), &ctx), XcmError::TooExpensive);
-
-			// We actually use half of the weight
-			let weight_used = bought / 2;
-
-			// Make sure refurnd works.
-			let amount_refunded = WeightToFee::weight_to_fee(&(bought - weight_used));
+			// refund.
+			let actual_refund = trader.refund_weight(refund_weight, &ctx).unwrap();
+			assert_eq!(actual_refund, (asset_1_location, asset_refund).into());
 
+			// assert.
+			assert_eq!(Balances::balance(&staking_pot), initial_balance);
+			// only after `trader` is dropped we expect the fee to be resolved into the treasury
+			// account.
+			drop(trader);
+			assert_eq!(Balances::balance(&staking_pot), initial_balance + fee - refund);
 			assert_eq!(
-				trader.refund_weight(bought - weight_used, &ctx),
-				Some((asset_multilocation, amount_refunded).into())
+				Assets::total_issuance(asset_1),
+				asset_total_issuance + asset_fee - asset_refund
 			);
+			assert_eq!(Balances::total_issuance(), native_total_issuance);
+		})
+}
 
-			// Drop trader
-			drop(trader);
+#[test]
+fn test_buy_and_refund_weight_with_swap_foreign_asset_xcm_trader() {
+	ExtBuilder::<Runtime>::default()
+		.with_collators(vec![AccountId::from(ALICE)])
+		.with_session_keys(vec![(
+			AccountId::from(ALICE),
+			AccountId::from(ALICE),
+			SessionKeys { aura: AuraId::from(sp_core::sr25519::Public::from_raw(ALICE)) },
+		)])
+		.build()
+		.execute_with(|| {
+			let bob: AccountId = SOME_ASSET_ADMIN.into();
+			let staking_pot = CollatorSelection::account_id();
+			let native_location = WestendLocation::get();
+			let foreign_location =
+				MultiLocation { parents: 1, interior: X2(Parachain(1234), GeneralIndex(12345)) };
+			// bob's initial balance for native and `asset1` assets.
+			let initial_balance = 200 * UNITS;
+			// liquidity for both arms of (native, asset1) pool.
+			let pool_liquidity = 100 * UNITS;
 
-			// We only should have paid for half of the bought weight
-			let fees_paid = WeightToFee::weight_to_fee(&weight_used);
+			// init asset, balances and pool.
+			assert_ok!(<ForeignAssets as Create<_>>::create(
+				foreign_location,
+				bob.clone(),
+				true,
+				10
+			));
 
+			assert_ok!(ForeignAssets::mint_into(foreign_location, &bob, initial_balance));
+			assert_ok!(Balances::mint_into(&bob, initial_balance));
+			assert_ok!(Balances::mint_into(&staking_pot, initial_balance));
+
+			assert_ok!(AssetConversion::create_pool(
+				RuntimeHelper::origin_of(bob.clone()),
+				Box::new(native_location),
+				Box::new(foreign_location)
+			));
+
+			assert_ok!(AssetConversion::add_liquidity(
+				RuntimeHelper::origin_of(bob.clone()),
+				Box::new(native_location),
+				Box::new(foreign_location),
+				pool_liquidity,
+				pool_liquidity,
+				1,
+				1,
+				bob,
+			));
+
+			// keep initial total issuance to assert later.
+			let asset_total_issuance = ForeignAssets::total_issuance(foreign_location);
+			let native_total_issuance = Balances::total_issuance();
+
+			// prepare input to buy weight.
+			let weight = Weight::from_parts(4_000_000_000, 0);
+			let fee = WeightToFee::weight_to_fee(&weight);
+			let asset_fee =
+				AssetConversion::get_amount_in(&fee, &pool_liquidity, &pool_liquidity).unwrap();
+			let extra_amount = 100;
+			let ctx = XcmContext { origin: None, message_id: XcmHash::default(), topic: None };
+			let payment: MultiAsset = (foreign_location, asset_fee + extra_amount).into();
+
+			// init trader and buy weight.
+			let mut trader = <XcmConfig as xcm_executor::Config>::Trader::new();
+			let unused_asset =
+				trader.buy_weight(weight, payment.into(), &ctx).expect("Expected Ok");
+
+			// assert.
+			let unused_amount =
+				unused_asset.fungible.get(&foreign_location.into()).map_or(0, |a| *a);
+			assert_eq!(unused_amount, extra_amount);
 			assert_eq!(
-				Assets::balance(1, AccountId::from(ALICE)),
-				ExistentialDeposit::get() + fees_paid
+				ForeignAssets::total_issuance(foreign_location),
+				asset_total_issuance + asset_fee
 			);
 
-			// We also need to ensure the total supply increased
-			assert_eq!(Assets::total_supply(1), ExistentialDeposit::get() + fees_paid);
-		});
-}
+			// prepare input to refund weight.
+			let refund_weight = Weight::from_parts(1_000_000_000, 0);
+			let refund = WeightToFee::weight_to_fee(&refund_weight);
+			let (reserve1, reserve2) =
+				AssetConversion::get_reserves(native_location, foreign_location).unwrap();
+			let asset_refund =
+				AssetConversion::get_amount_out(&refund, &reserve1, &reserve2).unwrap();
 
-#[test]
-fn test_asset_xcm_trader_refund_not_possible_since_amount_less_than_ed() {
-	ExtBuilder::<Runtime>::default()
-		.with_collators(vec![AccountId::from(ALICE)])
-		.with_session_keys(vec![(
-			AccountId::from(ALICE),
-			AccountId::from(ALICE),
-			SessionKeys { aura: AuraId::from(sp_core::sr25519::Public::from_raw(ALICE)) },
-		)])
-		.build()
-		.execute_with(|| {
-			// We need root origin to create a sufficient asset
-			// We set existential deposit to be identical to the one for Balances first
-			assert_ok!(Assets::force_create(
-				RuntimeHelper::root_origin(),
-				1.into(),
-				AccountId::from(ALICE).into(),
-				true,
-				ExistentialDeposit::get()
-			));
+			// refund.
+			let actual_refund = trader.refund_weight(refund_weight, &ctx).unwrap();
+			assert_eq!(actual_refund, (foreign_location, asset_refund).into());
 
-			let mut trader = <XcmConfig as xcm_executor::Config>::Trader::new();
-			let ctx = XcmContext { origin: None, message_id: XcmHash::default(), topic: None };
-
-			// Set Alice as block author, who will receive fees
-			RuntimeHelper::run_to_block(2, AccountId::from(ALICE));
-
-			// We are going to buy small amount
-			let bought = Weight::from_parts(500_000_000u64, 0);
-
-			let asset_multilocation = AssetIdForTrustBackedAssetsConvert::convert_back(&1).unwrap();
-
-			let amount_bought = WeightToFee::weight_to_fee(&bought);
-
-			assert!(
-				amount_bought < ExistentialDeposit::get(),
-				"we are testing what happens when the amount does not exceed ED"
-			);
-
-			let asset: MultiAsset = (asset_multilocation, amount_bought).into();
-
-			// Buy weight should return an error
-			assert_noop!(trader.buy_weight(bought, asset.into(), &ctx), XcmError::TooExpensive);
-
-			// not credited since the ED is higher than this value
-			assert_eq!(Assets::balance(1, AccountId::from(ALICE)), 0);
-
-			// We also need to ensure the total supply did not increase
-			assert_eq!(Assets::total_supply(1), 0);
-		});
-}
-
-#[test]
-fn test_that_buying_ed_refund_does_not_refund() {
-	ExtBuilder::<Runtime>::default()
-		.with_collators(vec![AccountId::from(ALICE)])
-		.with_session_keys(vec![(
-			AccountId::from(ALICE),
-			AccountId::from(ALICE),
-			SessionKeys { aura: AuraId::from(sp_core::sr25519::Public::from_raw(ALICE)) },
-		)])
-		.build()
-		.execute_with(|| {
-			// We need root origin to create a sufficient asset
-			// We set existential deposit to be identical to the one for Balances first
-			assert_ok!(Assets::force_create(
-				RuntimeHelper::root_origin(),
-				1.into(),
-				AccountId::from(ALICE).into(),
-				true,
-				ExistentialDeposit::get()
-			));
-
-			let mut trader = <XcmConfig as xcm_executor::Config>::Trader::new();
-			let ctx = XcmContext { origin: None, message_id: XcmHash::default(), topic: None };
-
-			// Set Alice as block author, who will receive fees
-			RuntimeHelper::run_to_block(2, AccountId::from(ALICE));
-
-			let bought = Weight::from_parts(500_000_000u64, 0);
-
-			let asset_multilocation = AssetIdForTrustBackedAssetsConvert::convert_back(&1).unwrap();
-
-			let amount_bought = WeightToFee::weight_to_fee(&bought);
-
-			assert!(
-				amount_bought < ExistentialDeposit::get(),
-				"we are testing what happens when the amount does not exceed ED"
-			);
-
-			// We know we will have to buy at least ED, so lets make sure first it will
-			// fail with a payment of less than ED
-			let asset: MultiAsset = (asset_multilocation, amount_bought).into();
-			assert_noop!(trader.buy_weight(bought, asset.into(), &ctx), XcmError::TooExpensive);
-
-			// Now lets buy ED at least
-			let asset: MultiAsset = (asset_multilocation, ExistentialDeposit::get()).into();
-
-			// Buy weight should work
-			assert_ok!(trader.buy_weight(bought, asset.into(), &ctx));
-
-			// Should return None. We have a specific check making sure we dont go below ED for
-			// drop payment
-			assert_eq!(trader.refund_weight(bought, &ctx), None);
-
-			// Drop trader
+			// assert.
+			assert_eq!(Balances::balance(&staking_pot), initial_balance);
+			// only after `trader` is dropped we expect the fee to be resolved into the treasury
+			// account.
 			drop(trader);
-
-			// Make sure author(Alice) has received the amount
-			assert_eq!(Assets::balance(1, AccountId::from(ALICE)), ExistentialDeposit::get());
-
-			// We also need to ensure the total supply increased
-			assert_eq!(Assets::total_supply(1), ExistentialDeposit::get());
-		});
-}
-
-#[test]
-fn test_asset_xcm_trader_not_possible_for_non_sufficient_assets() {
-	ExtBuilder::<Runtime>::default()
-		.with_collators(vec![AccountId::from(ALICE)])
-		.with_session_keys(vec![(
-			AccountId::from(ALICE),
-			AccountId::from(ALICE),
-			SessionKeys { aura: AuraId::from(sp_core::sr25519::Public::from_raw(ALICE)) },
-		)])
-		.build()
-		.execute_with(|| {
-			// Create a non-sufficient asset with specific existential deposit
-			let minimum_asset_balance = 1_000_000_u128;
-			assert_ok!(Assets::force_create(
-				RuntimeHelper::root_origin(),
-				1.into(),
-				AccountId::from(ALICE).into(),
-				false,
-				minimum_asset_balance
-			));
-
-			// We first mint enough asset for the account to exist for assets
-			assert_ok!(Assets::mint(
-				RuntimeHelper::origin_of(AccountId::from(ALICE)),
-				1.into(),
-				AccountId::from(ALICE).into(),
-				minimum_asset_balance
-			));
-
-			let mut trader = <XcmConfig as xcm_executor::Config>::Trader::new();
-			let ctx = XcmContext { origin: None, message_id: XcmHash::default(), topic: None };
-
-			// Set Alice as block author, who will receive fees
-			RuntimeHelper::run_to_block(2, AccountId::from(ALICE));
-
-			// We are going to buy 4e9 weight
-			let bought = Weight::from_parts(4_000_000_000u64, 0);
-
-			// lets calculate amount needed
-			let asset_amount_needed = WeightToFee::weight_to_fee(&bought);
-
-			let asset_multilocation = AssetIdForTrustBackedAssetsConvert::convert_back(&1).unwrap();
-
-			let asset: MultiAsset = (asset_multilocation, asset_amount_needed).into();
-
-			// Make sure again buy_weight does return an error
-			assert_noop!(trader.buy_weight(bought, asset.into(), &ctx), XcmError::TooExpensive);
-
-			// Drop trader
-			drop(trader);
-
-			// Make sure author(Alice) has NOT received the amount
-			assert_eq!(Assets::balance(1, AccountId::from(ALICE)), minimum_asset_balance);
-
-			// We also need to ensure the total supply NOT increased
-			assert_eq!(Assets::total_supply(1), minimum_asset_balance);
-		});
+			assert_eq!(Balances::balance(&staking_pot), initial_balance + fee - refund);
+			assert_eq!(
+				ForeignAssets::total_issuance(foreign_location),
+				asset_total_issuance + asset_fee - asset_refund
+			);
+			assert_eq!(Balances::total_issuance(), native_total_issuance);
+		})
 }
 
 #[test]