Split SolutionImprovementThresholds into two types (#11221)

* Splitting `SolutionImprovementThreshold` in 2
One for Signed phase and one for Unsigned phase.

* Adding some tests

* Fixes after code review.
- Removing `GetDefault`.
- Shorter naming.
- More explicit test.

substrate/frame/election-provider-multi-phase/src/signed.rs

@@ -291,7 +291,7 @@ impl<T: Config> SignedSubmissions<T> {
 					None => return InsertResult::NotInserted,
 					Some((score, _)) => *score,
 				};
-				let threshold = T::SolutionImprovementThreshold::get();
+				let threshold = T::BetterSignedThreshold::get();
 
 				// if we haven't improved on the weakest score, don't change anything.
 				if !insert_score.strict_threshold_better(weakest_score, threshold) {
@@ -499,7 +499,7 @@ mod tests {
 			balances, raw_solution, roll_to, ExtBuilder, MultiPhase, Origin, Runtime,
 			SignedMaxSubmissions, SignedMaxWeight,
 		},
-		Error, Phase,
+		Error, Perbill, Phase,
 	};
 	use frame_support::{assert_noop, assert_ok, assert_storage_noop};
 
@@ -632,6 +632,54 @@ mod tests {
 		})
 	}
 
+	#[test]
+	fn cannot_submit_worse_with_full_queue_depends_on_threshold() {
+		ExtBuilder::default()
+			.signed_max_submission(1)
+			.better_signed_threshold(Perbill::from_percent(20))
+			.build_and_execute(|| {
+				roll_to(15);
+				assert!(MultiPhase::current_phase().is_signed());
+
+				let mut solution = RawSolution {
+					score: ElectionScore {
+						minimal_stake: 5u128,
+						sum_stake: 0u128,
+						sum_stake_squared: 10u128,
+					},
+					..Default::default()
+				};
+				assert_ok!(MultiPhase::submit(Origin::signed(99), Box::new(solution)));
+
+				// This is 10% better, so does not meet the 20% threshold and is therefore rejected.
+				solution = RawSolution {
+					score: ElectionScore {
+						minimal_stake: 5u128,
+						sum_stake: 0u128,
+						sum_stake_squared: 9u128,
+					},
+					..Default::default()
+				};
+
+				assert_noop!(
+					MultiPhase::submit(Origin::signed(99), Box::new(solution)),
+					Error::<Runtime>::SignedQueueFull,
+				);
+
+				// This is however 30% better and should therefore be accepted.
+				solution = RawSolution {
+					score: ElectionScore {
+						minimal_stake: 5u128,
+						sum_stake: 0u128,
+						sum_stake_squared: 7u128,
+					},
+					..Default::default()
+				};
+
+				assert_ok!(MultiPhase::submit(Origin::signed(99), Box::new(solution)));
+			})
+	}
+
 	#[test]
 	fn weakest_is_removed_if_better_provided() {
 		ExtBuilder::default().build_and_execute(|| {