Final answer:
A testament given under oath and written down before the trial is known as a pretrial deposition, which is part of pre-trial discovery used to prepare for the case.
Step-by-step explanation:
The testimony of a witness under oath that is written down before the trial for possible use when the case comes to trial is known as a pretrial deposition. This process is part of the pre-trial discovery, where both parties in a case have the opportunity to obtain evidence from the other party through various means such as depositions, interrogatories, and requests for admission. A pretrial deposition allows for thorough preparation for the case by both sides. It helps preserve testimony, enables lawyers to assess the witness's credibility and may also be used in court if the witness is unavailable to testify in person. It is important to understand that depositions are taken under oath and the witness is subject to cross-examination, similar to the proceedings during an actual trial.