public void AddAndGetExistingUserOk()
        {
            const string user1 = "user_A";
            const string user2 = "user_B";
            const string user3 = "user_C";
            var followingRepository = new FollowingRepository();

            // Precondition
            followingRepository.Add(user1, user2);

            followingRepository.Add(user1, user3);

            var expected = new List<string> { user2, user3 };
            var actual = followingRepository.Get(user1).ToList();

            CollectionAssert.AreEqual(expected, actual);
        }
        public void AddAndGetTwoNewUsersOk()
        {
            const string user1 = "user_A";
            const string user2 = "user_B";
            const string user3 = "user_C";
            var followingRepository = new FollowingRepository();

            followingRepository.Add(user1, user3);
            followingRepository.Add(user2, user3);

            var expected1 = new List<string> { user3 };
            var actual1 = followingRepository.Get(user1).ToList();
            CollectionAssert.AreEqual(expected1, actual1);

            var expected2 = new List<string> { user3 };
            var actual2 = followingRepository.Get(user1).ToList();
            CollectionAssert.AreEqual(expected2, actual2);
        }