add a new unit test for extrinsic pool (#611)

substrate/substrate/extrinsic-pool/src/rotator.rs

@@ -164,4 +164,39 @@ mod tests {
 		// then
 		assert!(!rotator.is_banned(&hash));
 	}
+
+	#[test]
+	fn should_garbage_collect() {
+		// given
+		fn tx_with(i: u64, time: Instant) -> Verified<u64, VerifiedTransaction> {
+			let hash = i.into();
+			Verified {
+				original: i,
+				verified: VerifiedTransaction {
+					hash,
+					sender: Default::default(),
+					nonce: Default::default(),
+				},
+				valid_till: time,
+			}
+		}
+
+		let rotator = rotator();
+
+		let now = Instant::now();
+		let past = now - Duration::from_secs(1);
+
+		// when
+		for i in 0..2*EXPECTED_SIZE {
+			let tx = tx_with(i as u64, past);
+			assert!(rotator.ban_if_stale(&now, &tx));
+		}
+		assert_eq!(rotator.banned_until.read().len(), 2*EXPECTED_SIZE);
+
+		// then
+		let tx = tx_with(2*EXPECTED_SIZE as u64, past);
+		// trigger a garbage collection
+		assert!(rotator.ban_if_stale(&now, &tx));
+		assert_eq!(rotator.banned_until.read().len(), EXPECTED_SIZE);
+	}
 }