Serena Williams has been drug tested more than anyone else and she wonders why! Serena’s sister Venus, Sloane Stephens and Madison Keys have been tested once. Serena says: “She has committed to five out of five competition tests in 2018. U.S. Open champion Sloane Stephens and U.S. 2017 Madison Keys have been tested once off the tour. Serena and Coco Vandeweghe have had two tests while not on the tour. Why so many for Serena?