• Sun tested positive for trimetazidine at national championships• China Anti-Doping Agency says three months is reasonable• China’s swimmers staggered the world at London 2012China’s world and Olympic swimming champion Sun Yang served a three-month ban for a failed doping test earlier this year, the China Anti-Doping Agency (Chinada) said on Monday.The agency said Sun had tested positive for trimetazidine, a stimulant that was added to the World Anti-Doping Agency’s (Wada) banned list this year.