Test storage removal leads to removal of stroage

substrate/runtime/staking/src/tests.rs

@@ -585,3 +585,35 @@ fn transferring_incomplete_reserved_balance_should_work() {
 		assert_eq!(Staking::free_balance(&2), 42);
 	});
 }
+
+#[test]
+fn account_removal_removes_storage() {
+	with_externalities(&mut new_test_ext(100, 1, 3, 1, false, 0), || {
+		// Setup two accounts with free balance above than exsistential threshold.
+		{
+			<FreeBalance<Test>>::insert(1, 110);
+			<StorageOf<Test>>::insert(1, b"foo".to_vec(), b"1".to_vec());
+			<StorageOf<Test>>::insert(1, b"bar".to_vec(), b"2".to_vec());
+
+			<FreeBalance<Test>>::insert(2, 110);
+			<StorageOf<Test>>::insert(2, b"hello".to_vec(), b"3".to_vec());
+			<StorageOf<Test>>::insert(2, b"world".to_vec(), b"4".to_vec());
+		}
+
+		// Transfer funds from account 1 of such amount that after this transfer
+		// the balance of account 1 is will be below than exsistential threshold.
+		//
+		// This should lead to the removal of all storage associated with this account.
+		Staking::transfer(&1, 2.into(), 20);
+
+		// Verify that all entries from account 1 is removed, while
+		// entries from account 2 is in place.
+		{
+			assert_eq!(<StorageOf<Test>>::get(1, b"foo".to_vec()), None);
+			assert_eq!(<StorageOf<Test>>::get(1, b"bar".to_vec()), None);
+
+			assert_eq!(<StorageOf<Test>>::get(2, b"hello".to_vec()), Some(b"3".to_vec()));
+			assert_eq!(<StorageOf<Test>>::get(2, b"world".to_vec()), Some(b"4".to_vec()));
+		}
+	});
+}