Improve Penpal runtime + emulated tests (#3543)

Issues addressed in this PR:
- Improve *Penpal* runtime:
- Properly handled received assets. Previously, it treated `(1, Here)`
as the local native currency, whereas it should be treated as a
`ForeignAsset`. This wasn't a great example of standard Parachain
behaviour, as no Parachain treats the system asset as the local
currency.
- Remove `AllowExplicitUnpaidExecutionFrom` the system. Again, this
wasn't a great example of standard Parachain behaviour.
- Move duplicated
`ForeignAssetFeeAsExistentialDepositMultiplierFeeCharger` to
`assets_common` crate.
- Improve emulated tests:
  - Update *Penpal* tests to new runtime.
- To simplify tests, register the reserve transferred, teleported, and
system assets in *Penpal* and *AssetHub* genesis. This saves us from
having to create the assets repeatedly for each test
- Add missing test case:
`reserve_transfer_assets_from_para_to_system_para`.
  - Cleanup.
- Prevent integration tests crates imports from being re-exported, as
they were polluting the `polkadot-sdk` docs.

There is still a test case missing for reserve transfers:
- Reserve transfer of system asset from *Parachain* to *Parachain*
trough *AssetHub*.
- This is not yet possible with `pallet-xcm` due to the reasons
explained in https://github.com/paritytech/polkadot-sdk/pull/3339

---------

Co-authored-by: command-bot <>

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-rococo/src/lib.rs

@@ -13,62 +13,53 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Substrate
-pub use frame_support::{assert_err, assert_ok, pallet_prelude::DispatchResult};
-pub use sp_runtime::DispatchError;
+#[cfg(test)]
+mod imports {
+	// Substrate
+	pub use frame_support::{assert_err, assert_ok, pallet_prelude::DispatchResult};
+	pub use sp_runtime::DispatchError;
 
-// Polkadot
-pub use xcm::{
-	latest::ParentThen,
-	prelude::{AccountId32 as AccountId32Junction, *},
-	v3::{
-		self, Error,
-		NetworkId::{Rococo as RococoId, Westend as WestendId},
-	},
-};
+	// Polkadot
+	pub use xcm::{
+		latest::ParentThen,
+		prelude::{AccountId32 as AccountId32Junction, *},
+		v3::{self, NetworkId::Westend as WestendId},
+	};
 
-// Bridges
-pub use bp_messages::LaneId;
+	// Cumulus
+	pub use emulated_integration_tests_common::{
+		accounts::ALICE,
+		impls::Inspect,
+		test_parachain_is_trusted_teleporter,
+		xcm_emulator::{
+			assert_expected_events, bx, Chain, Parachain as Para, RelayChain as Relay, TestExt,
+		},
+	};
+	pub use parachains_common::AccountId;
+	pub use rococo_westend_system_emulated_network::{
+		asset_hub_rococo_emulated_chain::{
+			genesis::ED as ASSET_HUB_ROCOCO_ED, AssetHubRococoParaPallet as AssetHubRococoPallet,
+		},
+		asset_hub_westend_emulated_chain::{
+			genesis::ED as ASSET_HUB_WESTEND_ED, AssetHubWestendParaPallet as AssetHubWestendPallet,
+		},
+		bridge_hub_rococo_emulated_chain::{
+			genesis::ED as BRIDGE_HUB_ROCOCO_ED, BridgeHubRococoParaPallet as BridgeHubRococoPallet,
+		},
+		penpal_emulated_chain::PenpalAParaPallet as PenpalAPallet,
+		rococo_emulated_chain::{genesis::ED as ROCOCO_ED, RococoRelayPallet as RococoPallet},
+		AssetHubRococoPara as AssetHubRococo, AssetHubRococoParaReceiver as AssetHubRococoReceiver,
+		AssetHubRococoParaSender as AssetHubRococoSender, AssetHubWestendPara as AssetHubWestend,
+		AssetHubWestendParaReceiver as AssetHubWestendReceiver,
+		AssetHubWestendParaSender as AssetHubWestendSender, BridgeHubRococoPara as BridgeHubRococo,
+		BridgeHubRococoParaSender as BridgeHubRococoSender,
+		BridgeHubWestendPara as BridgeHubWestend, PenpalAPara as PenpalA,
+		PenpalAParaReceiver as PenpalAReceiver, PenpalAParaSender as PenpalASender,
+		RococoRelay as Rococo,
+	};
 
-// Cumulus
-pub use emulated_integration_tests_common::{
-	accounts::ALICE,
-	impls::Inspect,
-	test_parachain_is_trusted_teleporter,
-	xcm_emulator::{
-		assert_expected_events, bx, helpers::weight_within_threshold, Chain, Parachain as Para,
-		RelayChain as Relay, Test, TestArgs, TestContext, TestExt,
-	},
-	xcm_helpers::{xcm_transact_paid_execution, xcm_transact_unpaid_execution},
-	PROOF_SIZE_THRESHOLD, REF_TIME_THRESHOLD, XCM_V3,
-};
-pub use parachains_common::{AccountId, Balance};
-pub use rococo_westend_system_emulated_network::{
-	asset_hub_rococo_emulated_chain::{
-		genesis::ED as ASSET_HUB_ROCOCO_ED, AssetHubRococoParaPallet as AssetHubRococoPallet,
-	},
-	asset_hub_westend_emulated_chain::{
-		genesis::ED as ASSET_HUB_WESTEND_ED, AssetHubWestendParaPallet as AssetHubWestendPallet,
-	},
-	bridge_hub_rococo_emulated_chain::{
-		genesis::ED as BRIDGE_HUB_ROCOCO_ED, BridgeHubRococoParaPallet as BridgeHubRococoPallet,
-	},
-	penpal_emulated_chain::PenpalAParaPallet as PenpalAPallet,
-	rococo_emulated_chain::{genesis::ED as ROCOCO_ED, RococoRelayPallet as RococoPallet},
-	AssetHubRococoPara as AssetHubRococo, AssetHubRococoParaReceiver as AssetHubRococoReceiver,
-	AssetHubRococoParaSender as AssetHubRococoSender, AssetHubWestendPara as AssetHubWestend,
-	AssetHubWestendParaReceiver as AssetHubWestendReceiver,
-	AssetHubWestendParaSender as AssetHubWestendSender, BridgeHubRococoPara as BridgeHubRococo,
-	BridgeHubRococoParaReceiver as BridgeHubRococoReceiver,
-	BridgeHubRococoParaSender as BridgeHubRococoSender, BridgeHubWestendPara as BridgeHubWestend,
-	PenpalAPara as PenpalA, PenpalAParaReceiver as PenpalAReceiver,
-	PenpalAParaSender as PenpalASender, RococoRelay as Rococo,
-	RococoRelayReceiver as RococoReceiver, RococoRelaySender as RococoSender,
-};
-
-pub const ASSET_ID: u32 = 1;
-pub const ASSET_MIN_BALANCE: u128 = 1000;
-pub const ASSETS_PALLET_ID: u8 = 50;
+	pub const ASSET_MIN_BALANCE: u128 = 1000;
+}
 
 #[cfg(test)]
 mod tests;

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-rococo/src/tests/mod.rs

@@ -13,7 +13,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use crate::*;
+use crate::imports::*;
 
 mod asset_transfers;
 mod send_xcm;

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-rococo/src/tests/snowbridge.rs

@@ -12,7 +12,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-use crate::*;
+use crate::imports::*;
 use bridge_hub_rococo_runtime::{EthereumBeaconClient, EthereumInboundQueue, RuntimeOrigin};
 use codec::{Decode, Encode};
 use emulated_integration_tests_common::xcm_emulator::ConvertLocation;

cumulus/parachains/integration-tests/emulated/tests/bridges/bridge-hub-rococo/src/tests/teleport.rs

@@ -13,7 +13,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use crate::*;
+use crate::tests::*;
 use bridge_hub_rococo_runtime::xcm_config::XcmConfig;
 
 #[test]