public void ShouldBeAbleToUpdateUsersFirstName()
        {
            InMemoryStorage storage         = new InMemoryStorage();
            int             testedUserdId   = 5;
            string          testedFirstName = "test";
            UserModel       testUser        = new UserModel
            {
                Id        = testedUserdId,
                FirstName = testedFirstName,
                LastName  = "",
                Birthdate = DateTime.Now
            };

            var result      = storage.UpdateUser(testUser);
            var changedUser = storage.GetUsersList().FirstOrDefault(x => x.Id == testedUserdId);

            Assert.True(result);
            Assert.NotNull(changedUser);
            Assert.Equal(changedUser.FirstName, testedFirstName);
        }