Yellen testimony in focus for Wall Street By: CNBC.com News May 07, 2014 at 05:05 AM EDT U.S. stock index futures signaled a mixed Wall Street open on Wednesday ahead of Federal Reserve Chair Janet Yellen's congressional testimony. Read More >> Related Stocks: Alstom S.A. Facebook General Electric News Corporation Sentinelone Inc Cl A Tesla, Inc. Twenty-First Century Fox