lib.rs

				assert_ok!(ChargeTransactionPayment::<Runtime>::post_dispatch(
					pre,
					&info_from_weight(5),
					&default_post_info(),
					len,
					&Ok(())
				));
				assert_eq!(Balances::free_balance(1), 100 - 5 - 5 - 10);
				assert_eq!(FEE_UNBALANCED_AMOUNT.with(|a| a.borrow().clone()), 5 + 5 + 10);
				assert_eq!(TIP_UNBALANCED_AMOUNT.with(|a| a.borrow().clone()), 0);

				FEE_UNBALANCED_AMOUNT.with(|a| *a.borrow_mut() = 0);

				let pre = ChargeTransactionPayment::<Runtime>::from(5 /* tipped */)
					.pre_dispatch(&2, CALL, &info_from_weight(100), len)
					.unwrap();
				assert_eq!(Balances::free_balance(2), 200 - 5 - 10 - 100 - 5);

				assert_ok!(ChargeTransactionPayment::<Runtime>::post_dispatch(
					pre,
					&info_from_weight(100),
					&post_info_from_weight(50),
					len,
					&Ok(())
				));
				assert_eq!(Balances::free_balance(2), 200 - 5 - 10 - 50 - 5);
				assert_eq!(FEE_UNBALANCED_AMOUNT.with(|a| a.borrow().clone()), 5 + 10 + 50);
				assert_eq!(TIP_UNBALANCED_AMOUNT.with(|a| a.borrow().clone()), 5);
			});
	}

	#[test]
	fn signed_extension_transaction_payment_multiplied_refund_works() {
		ExtBuilder::default()
			.balance_factor(10)
			.base_weight(5)
			.build()
			.execute_with(|| {
				let len = 10;
				<NextFeeMultiplier<Runtime>>::put(Multiplier::saturating_from_rational(3, 2));

				let pre = ChargeTransactionPayment::<Runtime>::from(5 /* tipped */)
					.pre_dispatch(&2, CALL, &info_from_weight(100), len)
					.unwrap();
				// 5 base fee, 10 byte fee, 3/2 * 100 weight fee, 5 tip
				assert_eq!(Balances::free_balance(2), 200 - 5 - 10 - 150 - 5);

				assert_ok!(ChargeTransactionPayment::<Runtime>::post_dispatch(
					pre,
					&info_from_weight(100),
					&post_info_from_weight(50),
					len,
					&Ok(())
				));
				// 75 (3/2 of the returned 50 units of weight) is refunded
				assert_eq!(Balances::free_balance(2), 200 - 5 - 10 - 75 - 5);
			});
	}

	#[test]
	fn signed_extension_transaction_payment_is_bounded() {
		ExtBuilder::default().balance_factor(1000).byte_fee(0).build().execute_with(|| {
			// maximum weight possible
			assert_ok!(ChargeTransactionPayment::<Runtime>::from(0).pre_dispatch(
				&1,
				CALL,
				&info_from_weight(Weight::max_value()),
				10
			));
			// fee will be proportional to what is the actual maximum weight in the runtime.
			assert_eq!(
				Balances::free_balance(&1),
				(10000 - <Runtime as frame_system::Config>::BlockWeights::get().max_block) as u64
			);
		});
	}

	#[test]
	fn signed_extension_allows_free_transactions() {
		ExtBuilder::default()
			.base_weight(100)
			.balance_factor(0)
			.build()
			.execute_with(|| {
				// 1 ain't have a penny.
				assert_eq!(Balances::free_balance(1), 0);

				let len = 100;

				// This is a completely free (and thus wholly insecure/DoS-ridden) transaction.
				let operational_transaction = DispatchInfo {
					weight: 0,
					class: DispatchClass::Operational,
					pays_fee: Pays::No,
				};
				assert_ok!(ChargeTransactionPayment::<Runtime>::from(0).validate(
					&1,
					CALL,
					&operational_transaction,
					len
				));

				// like a InsecureFreeNormal
				let free_transaction =
					DispatchInfo { weight: 0, class: DispatchClass::Normal, pays_fee: Pays::Yes };
				assert_noop!(
					ChargeTransactionPayment::<Runtime>::from(0).validate(
						&1,
						CALL,
						&free_transaction,
						len
					),
					TransactionValidityError::Invalid(InvalidTransaction::Payment),
				);
			});
	}

	#[test]
	fn signed_ext_length_fee_is_also_updated_per_congestion() {
		ExtBuilder::default()
			.base_weight(5)
			.balance_factor(10)
			.build()
			.execute_with(|| {
				// all fees should be x1.5
				<NextFeeMultiplier<Runtime>>::put(Multiplier::saturating_from_rational(3, 2));
				let len = 10;

				assert_ok!(ChargeTransactionPayment::<Runtime>::from(10) // tipped
					.pre_dispatch(&1, CALL, &info_from_weight(3), len));
				assert_eq!(
					Balances::free_balance(1),
					100 // original
				- 10 // tip
				- 5 // base
				- 10 // len
				- (3 * 3 / 2) // adjusted weight
				);
			})
	}

	#[test]
	fn query_info_works() {
		let call = Call::Balances(BalancesCall::transfer { dest: 2, value: 69 });
		let origin = 111111;
		let extra = ();
		let xt = TestXt::new(call, Some((origin, extra)));
		let info = xt.get_dispatch_info();
		let ext = xt.encode();
		let len = ext.len() as u32;
		ExtBuilder::default().base_weight(5).weight_fee(2).build().execute_with(|| {
			// all fees should be x1.5
			<NextFeeMultiplier<Runtime>>::put(Multiplier::saturating_from_rational(3, 2));

			assert_eq!(
				TransactionPayment::query_info(xt, len),
				RuntimeDispatchInfo {
					weight: info.weight,
					class: info.class,
					partial_fee: 5 * 2 /* base * weight_fee */
						+ len as u64  /* len * 1 */
						+ info.weight.min(BlockWeights::get().max_block) as u64 * 2 * 3 / 2 /* weight */
				},
			);
		});
	}

	#[test]
	fn compute_fee_works_without_multiplier() {
		ExtBuilder::default()
			.base_weight(100)
			.byte_fee(10)
			.balance_factor(0)
			.build()
			.execute_with(|| {
				// Next fee multiplier is zero
				assert_eq!(<NextFeeMultiplier<Runtime>>::get(), Multiplier::one());

				// Tip only, no fees works
				let dispatch_info = DispatchInfo {
					weight: 0,
					class: DispatchClass::Operational,
					pays_fee: Pays::No,
				};
				assert_eq!(Pallet::<Runtime>::compute_fee(0, &dispatch_info, 10), 10);
				// No tip, only base fee works
				let dispatch_info = DispatchInfo {
					weight: 0,
					class: DispatchClass::Operational,
					pays_fee: Pays::Yes,
				};
				assert_eq!(Pallet::<Runtime>::compute_fee(0, &dispatch_info, 0), 100);
				// Tip + base fee works
				assert_eq!(Pallet::<Runtime>::compute_fee(0, &dispatch_info, 69), 169);
				// Len (byte fee) + base fee works
				assert_eq!(Pallet::<Runtime>::compute_fee(42, &dispatch_info, 0), 520);
				// Weight fee + base fee works
				let dispatch_info = DispatchInfo {
					weight: 1000,
					class: DispatchClass::Operational,
					pays_fee: Pays::Yes,
				};
				assert_eq!(Pallet::<Runtime>::compute_fee(0, &dispatch_info, 0), 1100);
			});
	}

	#[test]
	fn compute_fee_works_with_multiplier() {
		ExtBuilder::default()
			.base_weight(100)
			.byte_fee(10)
			.balance_factor(0)
			.build()
			.execute_with(|| {
				// Add a next fee multiplier. Fees will be x3/2.
				<NextFeeMultiplier<Runtime>>::put(Multiplier::saturating_from_rational(3, 2));
				// Base fee is unaffected by multiplier
				let dispatch_info = DispatchInfo {
					weight: 0,
					class: DispatchClass::Operational,
					pays_fee: Pays::Yes,
				};
				assert_eq!(Pallet::<Runtime>::compute_fee(0, &dispatch_info, 0), 100);

				// Everything works together :)
				let dispatch_info = DispatchInfo {
					weight: 123,
					class: DispatchClass::Operational,
					pays_fee: Pays::Yes,
				};
				// 123 weight, 456 length, 100 base
				assert_eq!(
					Pallet::<Runtime>::compute_fee(456, &dispatch_info, 789),
					100 + (3 * 123 / 2) + 4560 + 789,
				);
			});
	}

	#[test]
	fn compute_fee_works_with_negative_multiplier() {
		ExtBuilder::default()
			.base_weight(100)
			.byte_fee(10)
			.balance_factor(0)
			.build()
			.execute_with(|| {
				// Add a next fee multiplier. All fees will be x1/2.
				<NextFeeMultiplier<Runtime>>::put(Multiplier::saturating_from_rational(1, 2));

				// Base fee is unaffected by multiplier.
				let dispatch_info = DispatchInfo {
					weight: 0,
					class: DispatchClass::Operational,
					pays_fee: Pays::Yes,
				};
				assert_eq!(Pallet::<Runtime>::compute_fee(0, &dispatch_info, 0), 100);

				// Everything works together.
				let dispatch_info = DispatchInfo {
					weight: 123,
					class: DispatchClass::Operational,
					pays_fee: Pays::Yes,
				};
				// 123 weight, 456 length, 100 base
				assert_eq!(
					Pallet::<Runtime>::compute_fee(456, &dispatch_info, 789),
					100 + (123 / 2) + 4560 + 789,
				);
			});
	}

	#[test]
	fn compute_fee_does_not_overflow() {
		ExtBuilder::default()
			.base_weight(100)
			.byte_fee(10)
			.balance_factor(0)
			.build()
			.execute_with(|| {
				// Overflow is handled
				let dispatch_info = DispatchInfo {
					weight: Weight::max_value(),
					class: DispatchClass::Operational,
					pays_fee: Pays::Yes,
				};
				assert_eq!(
					Pallet::<Runtime>::compute_fee(u32::MAX, &dispatch_info, u64::MAX),
					u64::MAX
				);
			});
	}

	#[test]
	fn refund_does_not_recreate_account() {
		ExtBuilder::default()
			.balance_factor(10)
			.base_weight(5)
			.build()
			.execute_with(|| {
				// So events are emitted
				System::set_block_number(10);
				let len = 10;
				let pre = ChargeTransactionPayment::<Runtime>::from(5 /* tipped */)
					.pre_dispatch(&2, CALL, &info_from_weight(100), len)
					.unwrap();
				assert_eq!(Balances::free_balance(2), 200 - 5 - 10 - 100 - 5);

				// kill the account between pre and post dispatch
				assert_ok!(Balances::transfer(Some(2).into(), 3, Balances::free_balance(2)));
				assert_eq!(Balances::free_balance(2), 0);

				assert_ok!(ChargeTransactionPayment::<Runtime>::post_dispatch(
					pre,
					&info_from_weight(100),
					&post_info_from_weight(50),
					len,
					&Ok(())
				));
				assert_eq!(Balances::free_balance(2), 0);
				// Transfer Event
				System::assert_has_event(Event::Balances(pallet_balances::Event::Transfer(
					2, 3, 80,
				)));
				// Killed Event
				System::assert_has_event(Event::System(system::Event::KilledAccount(2)));
			});
	}

	#[test]
	fn actual_weight_higher_than_max_refunds_nothing() {
		ExtBuilder::default()
			.balance_factor(10)
			.base_weight(5)
			.build()
			.execute_with(|| {
				let len = 10;
				let pre = ChargeTransactionPayment::<Runtime>::from(5 /* tipped */)
					.pre_dispatch(&2, CALL, &info_from_weight(100), len)
					.unwrap();
				assert_eq!(Balances::free_balance(2), 200 - 5 - 10 - 100 - 5);

				assert_ok!(ChargeTransactionPayment::<Runtime>::post_dispatch(
					pre,
					&info_from_weight(100),
					&post_info_from_weight(101),
					len,
					&Ok(())
				));
				assert_eq!(Balances::free_balance(2), 200 - 5 - 10 - 100 - 5);
			});
	}

	#[test]
	fn zero_transfer_on_free_transaction() {
		ExtBuilder::default()
			.balance_factor(10)
			.base_weight(5)
			.build()
			.execute_with(|| {
				// So events are emitted
				System::set_block_number(10);
				let len = 10;
				let dispatch_info =
					DispatchInfo { weight: 100, pays_fee: Pays::No, class: DispatchClass::Normal };
				let user = 69;
				let pre = ChargeTransactionPayment::<Runtime>::from(0)
					.pre_dispatch(&user, CALL, &dispatch_info, len)
					.unwrap();
				assert_eq!(Balances::total_balance(&user), 0);
				assert_ok!(ChargeTransactionPayment::<Runtime>::post_dispatch(
					pre,
					&dispatch_info,
					&default_post_info(),
					len,
					&Ok(())
				));
				assert_eq!(Balances::total_balance(&user), 0);
				// No events for such a scenario
				assert_eq!(System::events().len(), 0);
			});
	}

	#[test]
	fn refund_consistent_with_actual_weight() {
		ExtBuilder::default()
			.balance_factor(10)
			.base_weight(7)
			.build()
			.execute_with(|| {
				let info = info_from_weight(100);
				let post_info = post_info_from_weight(33);
				let prev_balance = Balances::free_balance(2);
				let len = 10;
				let tip = 5;

				<NextFeeMultiplier<Runtime>>::put(Multiplier::saturating_from_rational(5, 4));

				let pre = ChargeTransactionPayment::<Runtime>::from(tip)
					.pre_dispatch(&2, CALL, &info, len)
					.unwrap();

				ChargeTransactionPayment::<Runtime>::post_dispatch(
					pre,
					&info,
					&post_info,
					len,
					&Ok(()),
				)
				.unwrap();

				let refund_based_fee = prev_balance - Balances::free_balance(2);
				let actual_fee =
					Pallet::<Runtime>::compute_actual_fee(len as u32, &info, &post_info, tip);

				// 33 weight, 10 length, 7 base, 5 tip
				assert_eq!(actual_fee, 7 + 10 + (33 * 5 / 4) + 5);
				assert_eq!(refund_based_fee, actual_fee);
			});
	}

	#[test]
	fn should_alter_operational_priority() {
		let tip = 5;
		let len = 10;

		ExtBuilder::default().balance_factor(100).build().execute_with(|| {
			let normal =
				DispatchInfo { weight: 100, class: DispatchClass::Normal, pays_fee: Pays::Yes };
			let priority = ChargeTransactionPayment::<Runtime>(tip)
				.validate(&2, CALL, &normal, len)
				.unwrap()
				.priority;

			assert_eq!(priority, 50);

			let priority = ChargeTransactionPayment::<Runtime>(2 * tip)
				.validate(&2, CALL, &normal, len)
				.unwrap()
				.priority;

			assert_eq!(priority, 100);
		});

		ExtBuilder::default().balance_factor(100).build().execute_with(|| {
			let op = DispatchInfo {
				weight: 100,
				class: DispatchClass::Operational,
				pays_fee: Pays::Yes,
			};
			let priority = ChargeTransactionPayment::<Runtime>(tip)
				.validate(&2, CALL, &op, len)
				.unwrap()
				.priority;
			assert_eq!(priority, 5800);

			let priority = ChargeTransactionPayment::<Runtime>(2 * tip)
				.validate(&2, CALL, &op, len)
				.unwrap()
				.priority;
			assert_eq!(priority, 6100);
		});
	}

	#[test]
	fn no_tip_has_some_priority() {
		let tip = 0;
		let len = 10;

		ExtBuilder::default().balance_factor(100).build().execute_with(|| {
			let normal =
				DispatchInfo { weight: 100, class: DispatchClass::Normal, pays_fee: Pays::Yes };
			let priority = ChargeTransactionPayment::<Runtime>(tip)
				.validate(&2, CALL, &normal, len)
				.unwrap()
				.priority;

			assert_eq!(priority, 10);
		});

		ExtBuilder::default().balance_factor(100).build().execute_with(|| {
			let op = DispatchInfo {
				weight: 100,
				class: DispatchClass::Operational,
				pays_fee: Pays::Yes,
			};
			let priority = ChargeTransactionPayment::<Runtime>(tip)
				.validate(&2, CALL, &op, len)
				.unwrap()
				.priority;
			assert_eq!(priority, 5510);
		});
	}

	#[test]
	fn post_info_can_change_pays_fee() {
		ExtBuilder::default()
			.balance_factor(10)
			.base_weight(7)
			.build()
			.execute_with(|| {
				let info = info_from_weight(100);
				let post_info = post_info_from_pays(Pays::No);
				let prev_balance = Balances::free_balance(2);
				let len = 10;
				let tip = 5;

				<NextFeeMultiplier<Runtime>>::put(Multiplier::saturating_from_rational(5, 4));

				let pre = ChargeTransactionPayment::<Runtime>::from(tip)
					.pre_dispatch(&2, CALL, &info, len)
					.unwrap();

				ChargeTransactionPayment::<Runtime>::post_dispatch(
					pre,
					&info,
					&post_info,
					len,
					&Ok(()),
				)
				.unwrap();

				let refund_based_fee = prev_balance - Balances::free_balance(2);
				let actual_fee =
					Pallet::<Runtime>::compute_actual_fee(len as u32, &info, &post_info, tip);

				// Only 5 tip is paid
				assert_eq!(actual_fee, 5);
				assert_eq!(refund_based_fee, actual_fee);
			});
	}
}