Fix Session Benchmarks (paritytech#7476)

* Always remove validator bfore creating new ones

* remove comment

* update tests and docs

frame/staking/src/benchmarking.rs

@@ -45,14 +45,17 @@ fn add_slashing_spans<T: Trait>(who: &T::AccountId, spans: u32) {
 	SlashingSpans::<T>::insert(who, slashing_spans);
 }
 
-// This function generates one validator being nominated by n nominators, and returns the validator
-// stash account and the nominators' stash and controller. It also starts an era and creates pending payouts.
+// This function clears all existing validators and nominators from the set, and generates one new
+// validator being nominated by n nominators, and returns the validator stash account and the
+// nominators' stash and controller. It also starts an era and creates pending payouts.
 pub fn create_validator_with_nominators<T: Trait>(
 	n: u32,
 	upper_bound: u32,
 	dead: bool,
 	destination: RewardDestination<T::AccountId>
 ) -> Result<(T::AccountId, Vec<(T::AccountId, T::AccountId)>), &'static str> {
+	// Clean up any existing state.
+	clear_validators_and_nominators::<T>();
 	let mut points_total = 0;
 	let mut points_individual = Vec::new();
 
@@ -286,8 +289,6 @@ benchmarks! {
 
 	payout_stakers_dead_controller {
 		let n in 1 .. T::MaxNominatorRewardedPerValidator::get() as u32;
-		// Clean up existing validators
-		Validators::<T>::remove_all();
 		let (validator, nominators) = create_validator_with_nominators::<T>(
 			n,
 			T::MaxNominatorRewardedPerValidator::get() as u32,
@@ -321,8 +322,6 @@ benchmarks! {
 
 	payout_stakers_alive_staked {
 		let n in 1 .. T::MaxNominatorRewardedPerValidator::get() as u32;
-		// Clean up existing validators
-		Validators::<T>::remove_all();
 		let (validator, nominators) = create_validator_with_nominators::<T>(
 			n,
 			T::MaxNominatorRewardedPerValidator::get() as u32,
@@ -708,7 +707,7 @@ mod tests {
 
 	#[test]
 	fn create_validators_with_nominators_for_era_works() {
-		ExtBuilder::default().has_stakers(false).build().execute_with(|| {
+		ExtBuilder::default().has_stakers(true).build().execute_with(|| {
 			let v = 10;
 			let n = 100;
 
@@ -725,7 +724,7 @@ mod tests {
 
 	#[test]
 	fn create_validator_with_nominators_works() {
-		ExtBuilder::default().has_stakers(false).build().execute_with(|| {
+		ExtBuilder::default().has_stakers(true).build().execute_with(|| {
 			let n = 10;
 
 			let (validator_stash, nominators) = create_validator_with_nominators::<Test>(
@@ -749,7 +748,7 @@ mod tests {
 
 	#[test]
 	fn add_slashing_spans_works() {
-		ExtBuilder::default().has_stakers(false).build().execute_with(|| {
+		ExtBuilder::default().has_stakers(true).build().execute_with(|| {
 			let n = 10;
 
 			let (validator_stash, _nominators) = create_validator_with_nominators::<Test>(
@@ -780,7 +779,7 @@ mod tests {
 
 	#[test]
 	fn test_payout_all() {
-		ExtBuilder::default().has_stakers(false).build().execute_with(|| {
+		ExtBuilder::default().has_stakers(true).build().execute_with(|| {
 			let v = 10;
 			let n = 100;
 
@@ -799,7 +798,7 @@ mod tests {
 
 	#[test]
 	fn test_benchmarks() {
-		ExtBuilder::default().has_stakers(false).build().execute_with(|| {
+		ExtBuilder::default().has_stakers(true).build().execute_with(|| {
 			assert_ok!(test_benchmark_bond::<Test>());
 			assert_ok!(test_benchmark_bond_extra::<Test>());
 			assert_ok!(test_benchmark_unbond::<Test>());

frame/staking/src/testing_utils.rs

@@ -28,6 +28,12 @@ use sp_npos_elections::*;
 
 const SEED: u32 = 0;
 
+/// This function removes all validators and nominators from storage.
+pub fn clear_validators_and_nominators<T: Trait>() {
+	Validators::<T>::remove_all();
+	Nominators::<T>::remove_all();
+}
+
 /// Grab a funded user.
 pub fn create_funded_user<T: Trait>(
 	string: &'static str,
@@ -97,6 +103,9 @@ pub fn create_validators<T: Trait>(
 /// This function generates validators and nominators who are randomly nominating
 /// `edge_per_nominator` random validators (until `to_nominate` if provided).
 ///
+/// NOTE: This function will remove any existing validators or nominators to ensure
+/// we are working with a clean state.
+///
 /// Parameters:
 /// - `validators`: number of bonded validators
 /// - `nominators`: number of bonded nominators.
@@ -113,6 +122,8 @@ pub fn create_validators_with_nominators_for_era<T: Trait>(
 	randomize_stake: bool,
 	to_nominate: Option<u32>,
 ) -> Result<Vec<<T::Lookup as StaticLookup>::Source>, &'static str> {
+	clear_validators_and_nominators::<T>();
+
 	let mut validators_stash: Vec<<T::Lookup as StaticLookup>::Source>
 		= Vec::with_capacity(validators as usize);
 	let mut rng = ChaChaRng::from_seed(SEED.using_encoded(blake2_256));