public void Test_Insert()
{
var user1 = new User("firstname1", "lastname1", 1, "id1");
var user2 = new User("firstname2", "lastname2", 2, "id2");
repository.Insert(user1);
repository.Insert(user2);
Assert.Equal(2, repository.Count());
Assert.Equal(user1, repository.GetByIdNumber("id1"));
Assert.Equal(user2, repository.GetByIdNumber("id2"));
}