The hearsay exception for prior testimony applies only if testimony was in fact previously given.

Cf. Valdez v. Winans, 738 F.2d 1087, pin? (10th Cir. 1984) (constitutional attack on use of privilege to exclude exculpatory evidence rejected under the circumstances).Although United States Supreme Court precedent establishes that in some circumstances a nonconstitutional privilege must yield to the federal constitutional rights of a criminal defendant, apart from the specific circumstances for which the Court has given an authoritative answer, it is unsettled and and it is unknown when such a privilege rule must yield to a federal constitutional right such as confrontation, due process, or the right to present a defense.

United States v. Johnson, 439 F.3d 947, 953 (8th Cir. 2006) (upholding trial court's admission of witness's testimony about his past crack cocaine dealings with the accused which was offered to show accused's knowledge, intent, or absence of mistake, where his past drug dealings were (1) "relevant to the...Evidence of a criminal or wrongful act apart from the act that at issue at trial Is not barred by the prohibition against circumstantial use of character if intent, knowledge, mistake, or accident is a legally-material factual issue, the opposing party suggests the non-existence of knowledge or urges mistake or accident as a defense, and evidence of another crime, wrong, or act is offered to prove the knowledge or the absence of mistake or accident by a criminal defendant or other person.

United States v. Hunt, 521 F.3d 636, 643 (6th Cir. 2008) (upholding trial court's refusal to admit the statements from an affidavit under Rule 804(b)(1) because "[defendant] has not demonstrated that the Government....The hearsay exception for prior testimony applies in a criminal trial or proceeding only if the prior testimony was given against the person who is now the defendant in the criminal proceeding or trial.