The term "testify" can be defined as the manner in which the oral statement is given in court, under affirmation or oath.
Testimony is usually given in response to the questions put forward by the attorneys at either a deposition (testimony given under oath but someplace outside the court), or at a trial.
Testify can also be explained as any statement made by a person, based on his or her personal knowledge of a fact.
The attorney of the opposing party has the right to cross-examine the witness by asking different questions about the answer that he or she has given as a testimony.