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/people/people-rococo/src/lib.rs

@@ -13,52 +13,41 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-pub use codec::Encode;
+#[cfg(test)]
+mod imports {
+	pub use codec::Encode;
 
-// Substrate
-pub use frame_support::{
-	assert_err, assert_ok,
-	pallet_prelude::Weight,
-	sp_runtime::{AccountId32, DispatchError, DispatchResult},
-	traits::fungibles::Inspect,
-};
+	// Substrate
+	pub use frame_support::{
+		assert_ok,
+		pallet_prelude::Weight,
+		sp_runtime::{AccountId32, DispatchResult},
+		traits::fungibles::Inspect,
+	};
 
-// Polkadot
-pub use xcm::{
-	prelude::{AccountId32 as AccountId32Junction, *},
-	v3::{Error, NetworkId::Rococo as RococoId},
-};
+	// Polkadot
+	pub use xcm::prelude::*;
 
-// Cumulus
-pub use asset_test_utils::xcm_helpers;
-pub use emulated_integration_tests_common::{
-	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_system_emulated_network::{
-	people_rococo_emulated_chain::{
-		genesis::ED as PEOPLE_ROCOCO_ED, PeopleRococoParaPallet as PeopleRococoPallet,
-	},
-	rococo_emulated_chain::{genesis::ED as ROCOCO_ED, RococoRelayPallet as RococoPallet},
-	PenpalAPara as PenpalA, PeopleRococoPara as PeopleRococo,
-	PeopleRococoParaReceiver as PeopleRococoReceiver, PeopleRococoParaSender as PeopleRococoSender,
-	RococoRelay as Rococo, RococoRelayReceiver as RococoReceiver,
-	RococoRelaySender as RococoSender,
-};
+	// Cumulus
+	pub use asset_test_utils::xcm_helpers;
+	pub use emulated_integration_tests_common::xcm_emulator::{
+		assert_expected_events, bx, Chain, Parachain as Para, RelayChain as Relay, Test, TestArgs,
+		TestContext, TestExt,
+	};
+	pub use parachains_common::Balance;
+	pub use rococo_system_emulated_network::{
+		people_rococo_emulated_chain::{
+			genesis::ED as PEOPLE_ROCOCO_ED, PeopleRococoParaPallet as PeopleRococoPallet,
+		},
+		rococo_emulated_chain::{genesis::ED as ROCOCO_ED, RococoRelayPallet as RococoPallet},
+		PeopleRococoPara as PeopleRococo, PeopleRococoParaReceiver as PeopleRococoReceiver,
+		PeopleRococoParaSender as PeopleRococoSender, RococoRelay as Rococo,
+		RococoRelayReceiver as RococoReceiver, RococoRelaySender as RococoSender,
+	};
 
-// pub const ASSET_ID: u32 = 1;
-// pub const ASSET_MIN_BALANCE: u128 = 1000;
-pub type RelayToSystemParaTest = Test<Rococo, PeopleRococo>;
-pub type RelayToParaTest = Test<Rococo, PenpalA>;
-pub type SystemParaToRelayTest = Test<PeopleRococo, Rococo>;
-pub type SystemParaToParaTest = Test<PeopleRococo, PenpalA>;
-pub type ParaToSystemParaTest = Test<PenpalA, PeopleRococo>;
+	pub type RelayToSystemParaTest = Test<Rococo, PeopleRococo>;
+	pub type SystemParaToRelayTest = Test<PeopleRococo, Rococo>;
+}
 
 #[cfg(test)]
 mod tests;

cumulus/parachains/integration-tests/emulated/tests/people/people-rococo/src/tests/reap_identity.rs

@@ -38,7 +38,7 @@
 //! - The freed deposit from the Relay Chain is sufficient for the parachain deposit; and
 //! - The account will exist on the parachain.
 
-use crate::*;
+use crate::imports::*;
 use frame_support::BoundedVec;
 use pallet_balances::Event as BalancesEvent;
 use pallet_identity::{legacy::IdentityInfo, Data, Event as IdentityEvent};

cumulus/parachains/integration-tests/emulated/tests/people/people-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::imports::*;
 use people_rococo_runtime::xcm_config::XcmConfig as PeopleRococoXcmConfig;
 use rococo_runtime::xcm_config::XcmConfig as RococoXcmConfig;