We noticed that if one solves this question as we intended, //length()// always returns +1 than the real length of the list (since it not allowed to modify it or any method of Linked_list other than __init__).
As a result, we will NOT include length() in our tests.
Our tests will include those methods that appear in the tests provided.
Sorry for any inconvenience regarding this,
[p.s. there might be a way around this, which we currently miss. If anyone does find such a solution, we will grant a 5 point bonus.]