pezkuwi-subxt/cumulus/pallets/collator-selection/src/tests.rs

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// 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 as collator_selection;
use crate::{
	mock::*, CandidacyBond, CandidateInfo, CandidateList, DesiredCandidates, Error, Invulnerables,
	LastAuthoredBlock,
};
use frame_support::{
	assert_noop, assert_ok,
	traits::{Currency, OnInitialize},
};
use pallet_balances::Error as BalancesError;
use sp_runtime::{testing::UintAuthorityId, traits::BadOrigin, BuildStorage};

#[test]
fn basic_setup_works() {
	new_test_ext().execute_with(|| {
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		// genesis should sort input
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);
	});
}

#[test]
fn it_should_set_invulnerables() {
	new_test_ext().execute_with(|| {
		let mut new_set = vec![1, 4, 3, 2];
		assert_ok!(CollatorSelection::set_invulnerables(
			RuntimeOrigin::signed(RootAccount::get()),
			new_set.clone()
		));
		new_set.sort();
		assert_eq!(Invulnerables::<Test>::get(), new_set);

		// cannot set with non-root.
		assert_noop!(
			CollatorSelection::set_invulnerables(RuntimeOrigin::signed(1), new_set),
			BadOrigin
		);
	});
}

#[test]
fn it_should_set_invulnerables_even_with_some_invalid() {
	new_test_ext().execute_with(|| {
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);
		let new_with_invalid = vec![1, 4, 3, 42, 2];

		assert_ok!(CollatorSelection::set_invulnerables(
			RuntimeOrigin::signed(RootAccount::get()),
			new_with_invalid
		));

		// should succeed and order them, but not include 42
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2, 3, 4]);
	});
}

#[test]
fn add_invulnerable_works() {
	new_test_ext().execute_with(|| {
		initialize_to_block(1);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);
		let new = 3;

		// function runs
		assert_ok!(CollatorSelection::add_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			new
		));

		System::assert_last_event(RuntimeEvent::CollatorSelection(
			crate::Event::InvulnerableAdded { account_id: new },
		));

		// same element cannot be added more than once
		assert_noop!(
			CollatorSelection::add_invulnerable(RuntimeOrigin::signed(RootAccount::get()), new),
			Error::<Test>::AlreadyInvulnerable
		);

		// new element is now part of the invulnerables list
		assert!(Invulnerables::<Test>::get().to_vec().contains(&new));

		// cannot add with non-root
		assert_noop!(CollatorSelection::add_invulnerable(RuntimeOrigin::signed(1), new), BadOrigin);

		// cannot add invulnerable without associated validator keys
		let not_validator = 42;
		assert_noop!(
			CollatorSelection::add_invulnerable(
				RuntimeOrigin::signed(RootAccount::get()),
				not_validator
			),
			Error::<Test>::ValidatorNotRegistered
		);
	});
}

#[test]
fn invulnerable_limit_works() {
	new_test_ext().execute_with(|| {
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// MaxInvulnerables: u32 = 20
		for ii in 3..=21 {
			// only keys were registered in mock for 1 to 5
			if ii > 5 {
				Balances::make_free_balance_be(&ii, 100);
				let key = MockSessionKeys { aura: UintAuthorityId(ii) };
				Session::set_keys(RuntimeOrigin::signed(ii).into(), key, Vec::new()).unwrap();
			}
			assert_eq!(Balances::free_balance(ii), 100);
			if ii < 21 {
				assert_ok!(CollatorSelection::add_invulnerable(
					RuntimeOrigin::signed(RootAccount::get()),
					ii
				));
			} else {
				assert_noop!(
					CollatorSelection::add_invulnerable(
						RuntimeOrigin::signed(RootAccount::get()),
						ii
					),
					Error::<Test>::TooManyInvulnerables
				);
			}
		}
		let expected: Vec<u64> = (1..=20).collect();
		assert_eq!(Invulnerables::<Test>::get(), expected);

		// Cannot set too many Invulnerables
		let too_many_invulnerables: Vec<u64> = (1..=21).collect();
		assert_noop!(
			CollatorSelection::set_invulnerables(
				RuntimeOrigin::signed(RootAccount::get()),
				too_many_invulnerables
			),
			Error::<Test>::TooManyInvulnerables
		);
		assert_eq!(Invulnerables::<Test>::get(), expected);
	});
}

#[test]
fn remove_invulnerable_works() {
	new_test_ext().execute_with(|| {
		initialize_to_block(1);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		assert_ok!(CollatorSelection::add_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			4
		));
		assert_ok!(CollatorSelection::add_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			3
		));

		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2, 3, 4]);

		assert_ok!(CollatorSelection::remove_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			2
		));

		System::assert_last_event(RuntimeEvent::CollatorSelection(
			crate::Event::InvulnerableRemoved { account_id: 2 },
		));
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 3, 4]);

		// cannot remove invulnerable not in the list
		assert_noop!(
			CollatorSelection::remove_invulnerable(RuntimeOrigin::signed(RootAccount::get()), 2),
			Error::<Test>::NotInvulnerable
		);

		// cannot remove without privilege
		assert_noop!(
			CollatorSelection::remove_invulnerable(RuntimeOrigin::signed(1), 3),
			BadOrigin
		);
	});
}

#[test]
fn candidate_to_invulnerable_works() {
	new_test_ext().execute_with(|| {
		initialize_to_block(1);
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(4), 100);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));

		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 90);

		assert_ok!(CollatorSelection::add_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			3
		));
		System::assert_has_event(RuntimeEvent::CollatorSelection(crate::Event::CandidateRemoved {
			account_id: 3,
		}));
		System::assert_has_event(RuntimeEvent::CollatorSelection(
			crate::Event::InvulnerableAdded { account_id: 3 },
		));
		assert!(Invulnerables::<Test>::get().to_vec().contains(&3));
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(CandidateList::<Test>::get().iter().count(), 1);

		assert_ok!(CollatorSelection::add_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			4
		));
		System::assert_has_event(RuntimeEvent::CollatorSelection(crate::Event::CandidateRemoved {
			account_id: 4,
		}));
		System::assert_has_event(RuntimeEvent::CollatorSelection(
			crate::Event::InvulnerableAdded { account_id: 4 },
		));
		assert!(Invulnerables::<Test>::get().to_vec().contains(&4));
		assert_eq!(Balances::free_balance(4), 100);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
	});
}

#[test]
fn set_desired_candidates_works() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);

		// can set
		assert_ok!(CollatorSelection::set_desired_candidates(
			RuntimeOrigin::signed(RootAccount::get()),
			7
		));
		assert_eq!(DesiredCandidates::<Test>::get(), 7);

		// rejects bad origin
		assert_noop!(
			CollatorSelection::set_desired_candidates(RuntimeOrigin::signed(1), 8),
			BadOrigin
		);
	});
}

#[test]
fn set_candidacy_bond_empty_candidate_list() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(CandidacyBond::<Test>::get(), 10);
		assert!(CandidateList::<Test>::get().is_empty());

		// can decrease without candidates
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			7
		));
		assert_eq!(CandidacyBond::<Test>::get(), 7);
		assert!(CandidateList::<Test>::get().is_empty());

		// rejects bad origin.
		assert_noop!(CollatorSelection::set_candidacy_bond(RuntimeOrigin::signed(1), 8), BadOrigin);

		// can increase without candidates
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			20
		));
		assert!(CandidateList::<Test>::get().is_empty());
		assert_eq!(CandidacyBond::<Test>::get(), 20);
	});
}

#[test]
fn set_candidacy_bond_with_one_candidate() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(CandidacyBond::<Test>::get(), 10);
		assert!(CandidateList::<Test>::get().is_empty());

		let candidate_3 = CandidateInfo { who: 3, deposit: 10 };

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_eq!(CandidateList::<Test>::get(), vec![candidate_3.clone()]);

		// can decrease with one candidate
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			7
		));
		assert_eq!(CandidacyBond::<Test>::get(), 7);
		assert_eq!(CandidateList::<Test>::get(), vec![candidate_3.clone()]);

		// can increase up to initial deposit
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			10
		));
		assert_eq!(CandidacyBond::<Test>::get(), 10);
		assert_eq!(CandidateList::<Test>::get(), vec![candidate_3.clone()]);

		// can increase past initial deposit, should kick existing candidate
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			20
		));
		assert!(CandidateList::<Test>::get().is_empty());
	});
}

#[test]
fn set_candidacy_bond_with_many_candidates_same_deposit() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(CandidacyBond::<Test>::get(), 10);
		assert!(CandidateList::<Test>::get().is_empty());

		let candidate_3 = CandidateInfo { who: 3, deposit: 10 };
		let candidate_4 = CandidateInfo { who: 4, deposit: 10 };
		let candidate_5 = CandidateInfo { who: 5, deposit: 10 };

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));
		assert_eq!(
			CandidateList::<Test>::get(),
			vec![candidate_5.clone(), candidate_4.clone(), candidate_3.clone()]
		);

		// can decrease with multiple candidates
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			7
		));
		assert_eq!(CandidacyBond::<Test>::get(), 7);
		assert_eq!(
			CandidateList::<Test>::get(),
			vec![candidate_5.clone(), candidate_4.clone(), candidate_3.clone()]
		);

		// can increase up to initial deposit
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			10
		));
		assert_eq!(CandidacyBond::<Test>::get(), 10);
		assert_eq!(
			CandidateList::<Test>::get(),
			vec![candidate_5.clone(), candidate_4.clone(), candidate_3.clone()]
		);

		// can increase past initial deposit, should kick existing candidates
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			20
		));
		assert!(CandidateList::<Test>::get().is_empty());
	});
}

#[test]
fn set_candidacy_bond_with_many_candidates_different_deposits() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(CandidacyBond::<Test>::get(), 10);
		assert!(CandidateList::<Test>::get().is_empty());

		let candidate_3 = CandidateInfo { who: 3, deposit: 10 };
		let candidate_4 = CandidateInfo { who: 4, deposit: 20 };
		let candidate_5 = CandidateInfo { who: 5, deposit: 30 };

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 30));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 20));
		assert_eq!(
			CandidateList::<Test>::get(),
			vec![candidate_3.clone(), candidate_4.clone(), candidate_5.clone()]
		);

		// can decrease with multiple candidates
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			7
		));
		assert_eq!(CandidacyBond::<Test>::get(), 7);
		assert_eq!(
			CandidateList::<Test>::get(),
			vec![candidate_3.clone(), candidate_4.clone(), candidate_5.clone()]
		);
		// can increase up to initial deposit
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			10
		));
		assert_eq!(CandidacyBond::<Test>::get(), 10);
		assert_eq!(
			CandidateList::<Test>::get(),
			vec![candidate_3.clone(), candidate_4.clone(), candidate_5.clone()]
		);

		// can increase to 4's deposit, should kick 3
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			20
		));
		assert_eq!(CandidacyBond::<Test>::get(), 20);
		assert_eq!(CandidateList::<Test>::get(), vec![candidate_4.clone(), candidate_5.clone()]);

		// can increase past 4's deposit, should kick 4
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			25
		));
		assert_eq!(CandidacyBond::<Test>::get(), 25);
		assert_eq!(CandidateList::<Test>::get(), vec![candidate_5.clone()]);

		// lowering the minimum deposit should have no effect
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			5
		));
		assert_eq!(CandidacyBond::<Test>::get(), 5);
		assert_eq!(CandidateList::<Test>::get(), vec![candidate_5.clone()]);

		// add 3 and 4 back but with higher deposits than minimum
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 10));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 20));
		assert_eq!(
			CandidateList::<Test>::get(),
			vec![candidate_3.clone(), candidate_4.clone(), candidate_5.clone()]
		);

		// can increase the deposit above the current max in the list, all candidates should be
		// kicked
		assert_ok!(CollatorSelection::set_candidacy_bond(
			RuntimeOrigin::signed(RootAccount::get()),
			40
		));
		assert_eq!(CandidacyBond::<Test>::get(), 40);
		assert!(CandidateList::<Test>::get().is_empty());
	});
}

#[test]
fn cannot_register_candidate_if_too_many() {
	new_test_ext().execute_with(|| {
		<crate::DesiredCandidates<Test>>::put(1);

		// MaxCandidates: u32 = 20
		// Aside from 3, 4, and 5, create enough accounts to have 21 potential
		// candidates.
		for i in 6..=23 {
			Balances::make_free_balance_be(&i, 100);
			let key = MockSessionKeys { aura: UintAuthorityId(i) };
			Session::set_keys(RuntimeOrigin::signed(i).into(), key, Vec::new()).unwrap();
		}

		for c in 3..=22 {
			assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(c)));
		}

		assert_noop!(
			CollatorSelection::register_as_candidate(RuntimeOrigin::signed(23)),
			Error::<Test>::TooManyCandidates,
		);
	})
}

#[test]
fn cannot_unregister_candidate_if_too_few() {
	new_test_ext().execute_with(|| {
		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);
		assert_ok!(CollatorSelection::remove_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			1
		));
		assert_noop!(
			CollatorSelection::remove_invulnerable(RuntimeOrigin::signed(RootAccount::get()), 2),
			Error::<Test>::TooFewEligibleCollators,
		);

		// reset desired candidates:
		<crate::DesiredCandidates<Test>>::put(1);
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));

		// now we can remove `2`
		assert_ok!(CollatorSelection::remove_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			2
		));

		// can not remove too few
		assert_noop!(
			CollatorSelection::leave_intent(RuntimeOrigin::signed(4)),
			Error::<Test>::TooFewEligibleCollators,
		);
	})
}

#[test]
fn cannot_register_as_candidate_if_invulnerable() {
	new_test_ext().execute_with(|| {
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// can't 1 because it is invulnerable.
		assert_noop!(
			CollatorSelection::register_as_candidate(RuntimeOrigin::signed(1)),
			Error::<Test>::AlreadyInvulnerable,
		);
	})
}

#[test]
fn cannot_register_as_candidate_if_keys_not_registered() {
	new_test_ext().execute_with(|| {
		// can't 7 because keys not registered.
		assert_noop!(
			CollatorSelection::register_as_candidate(RuntimeOrigin::signed(42)),
			Error::<Test>::ValidatorNotRegistered
		);
	})
}

#[test]
fn cannot_register_dupe_candidate() {
	new_test_ext().execute_with(|| {
		// can add 3 as candidate
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		// tuple of (id, deposit).
		let addition = CandidateInfo { who: 3, deposit: 10 };
		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![addition]
		);
		assert_eq!(LastAuthoredBlock::<Test>::get(3), 10);
		assert_eq!(Balances::free_balance(3), 90);

		// but no more
		assert_noop!(
			CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)),
			Error::<Test>::AlreadyCandidate,
		);
	})
}

#[test]
fn cannot_register_as_candidate_if_poor() {
	new_test_ext().execute_with(|| {
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(33), 0);

		// works
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));

		// poor
		assert_noop!(
			CollatorSelection::register_as_candidate(RuntimeOrigin::signed(33)),
			BalancesError::<Test>::InsufficientBalance,
		);
	});
}

#[test]
fn register_as_candidate_works() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// take two endowed, non-invulnerables accounts.
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(4), 100);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));

		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 90);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 2);
	});
}

#[test]
fn cannot_take_candidate_slot_if_invulnerable() {
	new_test_ext().execute_with(|| {
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// can't 1 because it is invulnerable.
		assert_noop!(
			CollatorSelection::take_candidate_slot(RuntimeOrigin::signed(1), 50u64.into(), 2),
			Error::<Test>::AlreadyInvulnerable,
		);
	})
}

#[test]
fn cannot_take_candidate_slot_if_keys_not_registered() {
	new_test_ext().execute_with(|| {
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_noop!(
			CollatorSelection::take_candidate_slot(RuntimeOrigin::signed(42), 50u64.into(), 3),
			Error::<Test>::ValidatorNotRegistered
		);
	})
}

#[test]
fn cannot_take_candidate_slot_if_duplicate() {
	new_test_ext().execute_with(|| {
		// can add 3 as candidate
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		// tuple of (id, deposit).
		let candidate_3 = CandidateInfo { who: 3, deposit: 10 };
		let candidate_4 = CandidateInfo { who: 4, deposit: 10 };
		let actual_candidates = CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>();
		assert_eq!(actual_candidates, vec![candidate_4, candidate_3]);
		assert_eq!(LastAuthoredBlock::<Test>::get(3), 10);
		assert_eq!(LastAuthoredBlock::<Test>::get(4), 10);
		assert_eq!(Balances::free_balance(3), 90);

		// but no more
		assert_noop!(
			CollatorSelection::take_candidate_slot(RuntimeOrigin::signed(3), 50u64.into(), 4),
			Error::<Test>::AlreadyCandidate,
		);
	})
}

#[test]
fn cannot_take_candidate_slot_if_target_invalid() {
	new_test_ext().execute_with(|| {
		// can add 3 as candidate
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		// tuple of (id, deposit).
		let candidate_3 = CandidateInfo { who: 3, deposit: 10 };
		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![candidate_3]
		);
		assert_eq!(LastAuthoredBlock::<Test>::get(3), 10);
		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 100);

		assert_noop!(
			CollatorSelection::take_candidate_slot(RuntimeOrigin::signed(4), 50u64.into(), 5),
			Error::<Test>::TargetIsNotCandidate,
		);
	})
}

#[test]
fn cannot_take_candidate_slot_if_poor() {
	new_test_ext().execute_with(|| {
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(33), 0);

		// works
		assert_ok!(CollatorSelection::take_candidate_slot(
			RuntimeOrigin::signed(3),
			20u64.into(),
			4
		));

		// poor
		assert_noop!(
			CollatorSelection::take_candidate_slot(RuntimeOrigin::signed(33), 30u64.into(), 3),
			BalancesError::<Test>::InsufficientBalance,
		);
	});
}

#[test]
fn cannot_take_candidate_slot_if_insufficient_deposit() {
	new_test_ext().execute_with(|| {
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 60u64.into()));
		assert_eq!(Balances::free_balance(3), 40);
		assert_eq!(Balances::free_balance(4), 100);
		assert_noop!(
			CollatorSelection::take_candidate_slot(RuntimeOrigin::signed(4), 5u64.into(), 3),
			Error::<Test>::InsufficientBond,
		);
		assert_eq!(Balances::free_balance(3), 40);
		assert_eq!(Balances::free_balance(4), 100);
	});
}

#[test]
fn cannot_take_candidate_slot_if_deposit_less_than_target() {
	new_test_ext().execute_with(|| {
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 60u64.into()));
		assert_eq!(Balances::free_balance(3), 40);
		assert_eq!(Balances::free_balance(4), 100);
		assert_noop!(
			CollatorSelection::take_candidate_slot(RuntimeOrigin::signed(4), 20u64.into(), 3),
			Error::<Test>::InsufficientBond,
		);
		assert_eq!(Balances::free_balance(3), 40);
		assert_eq!(Balances::free_balance(4), 100);
	});
}

#[test]
fn take_candidate_slot_works() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// take two endowed, non-invulnerables accounts.
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(4), 100);
		assert_eq!(Balances::free_balance(5), 100);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 90);
		assert_eq!(Balances::free_balance(5), 90);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);

		Balances::make_free_balance_be(&6, 100);
		let key = MockSessionKeys { aura: UintAuthorityId(6) };
		Session::set_keys(RuntimeOrigin::signed(6).into(), key, Vec::new()).unwrap();

		assert_ok!(CollatorSelection::take_candidate_slot(
			RuntimeOrigin::signed(6),
			50u64.into(),
			4
		));

		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 100);
		assert_eq!(Balances::free_balance(5), 90);
		assert_eq!(Balances::free_balance(6), 50);

		// tuple of (id, deposit).
		let candidate_3 = CandidateInfo { who: 3, deposit: 10 };
		let candidate_6 = CandidateInfo { who: 6, deposit: 50 };
		let candidate_5 = CandidateInfo { who: 5, deposit: 10 };
		let mut actual_candidates =
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>();
		actual_candidates.sort_by(|info_1, info_2| info_1.deposit.cmp(&info_2.deposit));
		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![candidate_5, candidate_3, candidate_6]
		);
	});
}

#[test]
fn increase_candidacy_bond_non_candidate_account() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));

		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(5), 20),
			Error::<Test>::NotCandidate
		);
	});
}

#[test]
fn increase_candidacy_bond_insufficient_balance() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// take two endowed, non-invulnerables accounts.
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(4), 100);
		assert_eq!(Balances::free_balance(5), 100);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 90);
		assert_eq!(Balances::free_balance(5), 90);

		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(3), 110),
			BalancesError::<Test>::InsufficientBalance
		);

		assert_eq!(Balances::free_balance(3), 90);
	});
}

#[test]
fn increase_candidacy_bond_works() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// take three endowed, non-invulnerables accounts.
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(4), 100);
		assert_eq!(Balances::free_balance(5), 100);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 90);
		assert_eq!(Balances::free_balance(5), 90);

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 20));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 30));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 40));

		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);
		assert_eq!(Balances::free_balance(3), 80);
		assert_eq!(Balances::free_balance(4), 70);
		assert_eq!(Balances::free_balance(5), 60);

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 40));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 60));

		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);
		assert_eq!(Balances::free_balance(3), 60);
		assert_eq!(Balances::free_balance(4), 40);
		assert_eq!(Balances::free_balance(5), 60);
	});
}

#[test]
fn decrease_candidacy_bond_non_candidate_account() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));

		assert_eq!(Balances::free_balance(5), 100);
		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(5), 10),
			Error::<Test>::NotCandidate
		);
		assert_eq!(Balances::free_balance(5), 100);
	});
}

#[test]
fn decrease_candidacy_bond_insufficient_funds() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// take two endowed, non-invulnerables accounts.
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(4), 100);
		assert_eq!(Balances::free_balance(5), 100);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 60));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 60));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 60));

		assert_eq!(Balances::free_balance(3), 40);
		assert_eq!(Balances::free_balance(4), 40);
		assert_eq!(Balances::free_balance(5), 40);

		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(3), 0),
			Error::<Test>::DepositTooLow
		);

		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(4), 5),
			Error::<Test>::DepositTooLow
		);

		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(5), 9),
			Error::<Test>::DepositTooLow
		);

		assert_eq!(Balances::free_balance(3), 40);
		assert_eq!(Balances::free_balance(4), 40);
		assert_eq!(Balances::free_balance(5), 40);
	});
}

#[test]
fn decrease_candidacy_bond_occupying_top_slot() {
	new_test_ext().execute_with(|| {
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		// Register 3 candidates.
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));
		// And update their bids.
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 30u64.into()));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 30u64.into()));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 60u64.into()));

		// tuple of (id, deposit).
		let candidate_3 = CandidateInfo { who: 3, deposit: 30 };
		let candidate_4 = CandidateInfo { who: 4, deposit: 30 };
		let candidate_5 = CandidateInfo { who: 5, deposit: 60 };
		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![candidate_4, candidate_3, candidate_5]
		);

		// Candidates 5 and 3 can't decrease their deposits because they are the 2 top candidates.
		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(5), 29),
			Error::<Test>::InvalidUnreserve,
		);
		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(3), 29),
			Error::<Test>::InvalidUnreserve,
		);
		// But candidate 4 should have be able to decrease the deposit up to the minimum.
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 29u64.into()));

		// Make candidate 4 outbid candidate 3, taking their spot as the second highest bid.
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 35u64.into()));

		// tuple of (id, deposit).
		let candidate_3 = CandidateInfo { who: 3, deposit: 30 };
		let candidate_4 = CandidateInfo { who: 4, deposit: 35 };
		let candidate_5 = CandidateInfo { who: 5, deposit: 60 };
		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![candidate_3, candidate_4, candidate_5]
		);

		// Now candidates 5 and 4 are the 2 top candidates, so they can't decrease their deposits.
		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(5), 34),
			Error::<Test>::InvalidUnreserve,
		);
		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(4), 34),
			Error::<Test>::InvalidUnreserve,
		);
		// Candidate 3 should have be able to decrease the deposit up to the minimum now that
		// they've fallen out of the top spots.
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 10u64.into()));
	});
}

#[test]
fn decrease_candidacy_bond_works() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// take three endowed, non-invulnerables accounts.
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(4), 100);
		assert_eq!(Balances::free_balance(5), 100);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 90);
		assert_eq!(Balances::free_balance(5), 90);

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 20));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 30));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 40));

		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);
		assert_eq!(Balances::free_balance(3), 80);
		assert_eq!(Balances::free_balance(4), 70);
		assert_eq!(Balances::free_balance(5), 60);

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 10));

		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);
		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 70);
		assert_eq!(Balances::free_balance(5), 60);
	});
}

#[test]
fn update_candidacy_bond_with_identical_amount() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// take three endowed, non-invulnerables accounts.
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(4), 100);
		assert_eq!(Balances::free_balance(5), 100);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 90);
		assert_eq!(Balances::free_balance(5), 90);

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 20));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 30));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 40));

		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);
		assert_eq!(Balances::free_balance(3), 80);
		assert_eq!(Balances::free_balance(4), 70);
		assert_eq!(Balances::free_balance(5), 60);

		assert_noop!(
			CollatorSelection::update_bond(RuntimeOrigin::signed(3), 20),
			Error::<Test>::IdenticalDeposit
		);
		assert_eq!(Balances::free_balance(3), 80);
	});
}

#[test]
fn candidate_list_works() {
	new_test_ext().execute_with(|| {
		// given
		assert_eq!(DesiredCandidates::<Test>::get(), 2);
		assert_eq!(CandidacyBond::<Test>::get(), 10);

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);

		// take three endowed, non-invulnerables accounts.
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(Balances::free_balance(4), 100);
		assert_eq!(Balances::free_balance(5), 100);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 20));

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 30));

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 25));

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 10));

		let candidate_3 = CandidateInfo { who: 3, deposit: 30 };
		let candidate_4 = CandidateInfo { who: 4, deposit: 25 };
		let candidate_5 = CandidateInfo { who: 5, deposit: 10 };
		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![candidate_5, candidate_4, candidate_3]
		);
	});
}

#[test]
fn leave_intent() {
	new_test_ext().execute_with(|| {
		// register a candidate.
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_eq!(Balances::free_balance(3), 90);

		// register too so can leave above min candidates
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));
		assert_eq!(Balances::free_balance(5), 90);

		// cannot leave if not candidate.
		assert_noop!(
			CollatorSelection::leave_intent(RuntimeOrigin::signed(4)),
			Error::<Test>::NotCandidate
		);

		// bond is returned
		assert_ok!(CollatorSelection::leave_intent(RuntimeOrigin::signed(3)));
		assert_eq!(Balances::free_balance(3), 100);
		assert_eq!(LastAuthoredBlock::<Test>::get(3), 0);
	});
}

#[test]
fn authorship_event_handler() {
	new_test_ext().execute_with(|| {
		// put 100 in the pot + 5 for ED
		Balances::make_free_balance_be(&CollatorSelection::account_id(), 105);

		// 4 is the default author.
		assert_eq!(Balances::free_balance(4), 100);
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		// triggers `note_author`
		Authorship::on_initialize(1);

		// tuple of (id, deposit).
		let collator = CandidateInfo { who: 4, deposit: 10 };

		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![collator]
		);
		assert_eq!(LastAuthoredBlock::<Test>::get(4), 0);

		// half of the pot goes to the collator who's the author (4 in tests).
		assert_eq!(Balances::free_balance(4), 140);
		// half + ED stays.
		assert_eq!(Balances::free_balance(CollatorSelection::account_id()), 55);
	});
}

#[test]
fn fees_edgecases() {
	new_test_ext().execute_with(|| {
		// Nothing panics, no reward when no ED in balance
		Authorship::on_initialize(1);
		// put some money into the pot at ED
		Balances::make_free_balance_be(&CollatorSelection::account_id(), 5);
		// 4 is the default author.
		assert_eq!(Balances::free_balance(4), 100);
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		// triggers `note_author`
		Authorship::on_initialize(1);

		// tuple of (id, deposit).
		let collator = CandidateInfo { who: 4, deposit: 10 };

		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![collator]
		);
		assert_eq!(LastAuthoredBlock::<Test>::get(4), 0);
		// Nothing received
		assert_eq!(Balances::free_balance(4), 90);
		// all fee stays
		assert_eq!(Balances::free_balance(CollatorSelection::account_id()), 5);
	});
}

#[test]
fn session_management_single_candidate() {
	new_test_ext().execute_with(|| {
		initialize_to_block(1);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(4);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		// add a new collator
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));

		// session won't see this.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);
		// but we have a new candidate.
		assert_eq!(CandidateList::<Test>::get().iter().count(), 1);

		initialize_to_block(10);
		assert_eq!(SessionChangeBlock::get(), 10);
		// pallet-session has 1 session delay; current validators are the same.
		assert_eq!(Session::validators(), vec![1, 2]);
		// queued ones are changed, and now we have 3.
		assert_eq!(Session::queued_keys().len(), 3);
		// session handlers (aura, et. al.) cannot see this yet.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(20);
		assert_eq!(SessionChangeBlock::get(), 20);
		// changed are now reflected to session handlers.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2, 3]);
	});
}

#[test]
fn session_management_max_candidates() {
	new_test_ext().execute_with(|| {
		initialize_to_block(1);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(4);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		// session won't see this.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);
		// but we have a new candidate.
		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);

		initialize_to_block(10);
		assert_eq!(SessionChangeBlock::get(), 10);
		// pallet-session has 1 session delay; current validators are the same.
		assert_eq!(Session::validators(), vec![1, 2]);
		// queued ones are changed, and now we have 4.
		assert_eq!(Session::queued_keys().len(), 4);
		// session handlers (aura, et. al.) cannot see this yet.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(20);
		assert_eq!(SessionChangeBlock::get(), 20);
		// changed are now reflected to session handlers.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2, 3, 4]);
	});
}

#[test]
fn session_management_increase_bid_with_list_update() {
	new_test_ext().execute_with(|| {
		initialize_to_block(1);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(4);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 60));

		// session won't see this.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);
		// but we have a new candidate.
		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);

		initialize_to_block(10);
		assert_eq!(SessionChangeBlock::get(), 10);
		// pallet-session has 1 session delay; current validators are the same.
		assert_eq!(Session::validators(), vec![1, 2]);
		// queued ones are changed, and now we have 4.
		assert_eq!(Session::queued_keys().len(), 4);
		// session handlers (aura, et. al.) cannot see this yet.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(20);
		assert_eq!(SessionChangeBlock::get(), 20);
		// changed are now reflected to session handlers.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2, 5, 3]);
	});
}

#[test]
fn session_management_candidate_list_eager_sort() {
	new_test_ext().execute_with(|| {
		initialize_to_block(1);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(4);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 60));

		// session won't see this.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);
		// but we have a new candidate.
		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);

		initialize_to_block(10);
		assert_eq!(SessionChangeBlock::get(), 10);
		// pallet-session has 1 session delay; current validators are the same.
		assert_eq!(Session::validators(), vec![1, 2]);
		// queued ones are changed, and now we have 4.
		assert_eq!(Session::queued_keys().len(), 4);
		// session handlers (aura, et. al.) cannot see this yet.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(20);
		assert_eq!(SessionChangeBlock::get(), 20);
		// changed are now reflected to session handlers.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2, 5, 3]);
	});
}

#[test]
fn session_management_reciprocal_outbidding() {
	new_test_ext().execute_with(|| {
		initialize_to_block(1);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(4);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 60));

		initialize_to_block(5);

		// candidates 3 and 4 saw they were outbid and preemptively bid more
		// than 5 in the next block.
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 70));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 70));

		// session won't see this.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);
		// but we have a new candidate.
		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);

		initialize_to_block(10);
		assert_eq!(SessionChangeBlock::get(), 10);
		// pallet-session has 1 session delay; current validators are the same.
		assert_eq!(Session::validators(), vec![1, 2]);
		// queued ones are changed, and now we have 4.
		assert_eq!(Session::queued_keys().len(), 4);
		// session handlers (aura, et. al.) cannot see this yet.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(20);
		assert_eq!(SessionChangeBlock::get(), 20);
		// changed are now reflected to session handlers.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2, 4, 3]);
	});
}

#[test]
fn session_management_decrease_bid_after_auction() {
	new_test_ext().execute_with(|| {
		initialize_to_block(1);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(4);

		assert_eq!(SessionChangeBlock::get(), 0);
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 60));

		initialize_to_block(5);

		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(4), 70));
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(3), 70));

		initialize_to_block(5);

		// candidate 5 saw it was outbid and wants to take back its bid, but
		// not entirely so they still keep their place in the candidate list
		// in case there is an opportunity in the future.
		assert_ok!(CollatorSelection::update_bond(RuntimeOrigin::signed(5), 10));

		// session won't see this.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);
		// but we have a new candidate.
		assert_eq!(CandidateList::<Test>::get().iter().count(), 3);

		initialize_to_block(10);
		assert_eq!(SessionChangeBlock::get(), 10);
		// pallet-session has 1 session delay; current validators are the same.
		assert_eq!(Session::validators(), vec![1, 2]);
		// queued ones are changed, and now we have 4.
		assert_eq!(Session::queued_keys().len(), 4);
		// session handlers (aura, et. al.) cannot see this yet.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2]);

		initialize_to_block(20);
		assert_eq!(SessionChangeBlock::get(), 20);
		// changed are now reflected to session handlers.
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2, 4, 3]);
	});
}

#[test]
fn kick_mechanism() {
	new_test_ext().execute_with(|| {
		// add a new collator
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		initialize_to_block(10);
		assert_eq!(CandidateList::<Test>::get().iter().count(), 2);
		initialize_to_block(20);
		assert_eq!(SessionChangeBlock::get(), 20);
		// 4 authored this block, gets to stay 3 was kicked
		assert_eq!(CandidateList::<Test>::get().iter().count(), 1);
		// 3 will be kicked after 1 session delay
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2, 3, 4]);
		// tuple of (id, deposit).
		let collator = CandidateInfo { who: 4, deposit: 10 };
		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![collator]
		);
		assert_eq!(LastAuthoredBlock::<Test>::get(4), 20);
		initialize_to_block(30);
		// 3 gets kicked after 1 session delay
		assert_eq!(SessionHandlerCollators::get(), vec![1, 2, 4]);
		// kicked collator gets funds back
		assert_eq!(Balances::free_balance(3), 100);
	});
}

#[test]
fn should_not_kick_mechanism_too_few() {
	new_test_ext().execute_with(|| {
		// remove the invulnerables and add new collators 3 and 5

		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2]);
		assert_ok!(CollatorSelection::remove_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			1
		));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(5)));
		assert_ok!(CollatorSelection::remove_invulnerable(
			RuntimeOrigin::signed(RootAccount::get()),
			2
		));

		initialize_to_block(10);
		assert_eq!(CandidateList::<Test>::get().iter().count(), 2);

		initialize_to_block(20);
		assert_eq!(SessionChangeBlock::get(), 20);
		// 4 authored this block, 3 is kicked, 5 stays because of too few collators
		assert_eq!(CandidateList::<Test>::get().iter().count(), 1);
		// 3 will be kicked after 1 session delay
		assert_eq!(SessionHandlerCollators::get(), vec![3, 5]);
		// tuple of (id, deposit).
		let collator = CandidateInfo { who: 3, deposit: 10 };
		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![collator]
		);
		assert_eq!(LastAuthoredBlock::<Test>::get(4), 20);

		initialize_to_block(30);
		// 3 gets kicked after 1 session delay
		assert_eq!(SessionHandlerCollators::get(), vec![3]);
		// kicked collator gets funds back
		assert_eq!(Balances::free_balance(5), 100);
	});
}

#[test]
fn should_kick_invulnerables_from_candidates_on_session_change() {
	new_test_ext().execute_with(|| {
		assert_eq!(CandidateList::<Test>::get().iter().count(), 0);
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(3)));
		assert_ok!(CollatorSelection::register_as_candidate(RuntimeOrigin::signed(4)));
		assert_eq!(Balances::free_balance(3), 90);
		assert_eq!(Balances::free_balance(4), 90);
		assert_ok!(CollatorSelection::set_invulnerables(
			RuntimeOrigin::signed(RootAccount::get()),
			vec![1, 2, 3]
		));

		// tuple of (id, deposit).
		let collator_3 = CandidateInfo { who: 3, deposit: 10 };
		let collator_4 = CandidateInfo { who: 4, deposit: 10 };

		let actual_candidates = CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>();
		assert_eq!(actual_candidates, vec![collator_4.clone(), collator_3]);
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2, 3]);

		// session change
		initialize_to_block(10);
		// 3 is removed from candidates
		assert_eq!(
			CandidateList::<Test>::get().iter().cloned().collect::<Vec<_>>(),
			vec![collator_4]
		);
		// but not from invulnerables
		assert_eq!(Invulnerables::<Test>::get(), vec![1, 2, 3]);
		// and it got its deposit back
		assert_eq!(Balances::free_balance(3), 100);
	});
}

#[test]
#[should_panic = "duplicate invulnerables in genesis."]
fn cannot_set_genesis_value_twice() {
	sp_tracing::try_init_simple();
	let mut t = frame_system::GenesisConfig::<Test>::default().build_storage().unwrap();
	let invulnerables = vec![1, 1];

	let collator_selection = collator_selection::GenesisConfig::<Test> {
		desired_candidates: 2,
		candidacy_bond: 10,
		invulnerables,
	};
	// collator selection must be initialized before session.
	collator_selection.assimilate_storage(&mut t).unwrap();
}