The jury made no judgements as to the efficacy of the tests. In fact, both the prosecution and the defense stipulated that the Theranos project was a failure. The defense even stated that "Failure is not fraud." The question before the jury was whether or not she had defrauded investors.

They decided that she had.

FWIW, every single firm that had medical expertise declined to invest in Theranos. They could see it had extremely minimal chance of success.