What is the legal test for a witness to testify in a wiretap case?

Mapping all the distinctions between such 'fruits of the poisonous tree' and a healthy harvest fir for court consumption is a task which has recently led even one distinguished commentator to throw up his hands in despair, see Amsterdam, Perspectives on the Fourth Amendment, 58 Minn.L.Rev. 349, 361 (1974). However, our previous decision in United States v. Tane,329 F.2d 848 (2d Cir. 1964), provides some guidance. In Tane, where a witness had agreed to testify after his identity had been discovered by an illegal wiretap and he had been

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