Is writing a will obligatory, is testimony required for it, and what is the legal text related to it?

The will should be written according to a formula that includes the Two Testimonies (Shahadatayn) and belief in the unseen, as well as an exhortation to family and relatives to fear Allah, to reconcile their differences, to obey Allah and His Messenger, to enjoin truth, and to persevere in it. Then, the testator mentions what he wishes to bequeath from a third of his wealth or less, specifies its legitimate expenditures, and names an executor for it. The will is commendable (mustahabb), unless the deceased has debts or rights that are not documented for their rightful owners, in which case he must make a will concerning them. Two just witnesses should attest to the will, and it should be drawn up by a reliable person among the people of knowledge.