General Motors Co Chief Executive Mary Barra said on Thursday the automaker will expand testing of self-driving vehicles to Michigan, and will build its next generation of self-driving cars in the Michigan plant that builds the Chevrolet Bolt electric car. Separately, Barra declined to discuss a statement by a Chinese government official that a U.S. automaker could be subject to penalties for price-fixing. “I don't think anyone benefits from speculating on that,” Barra told reporters at the event in GM's downtown Detroit headquarters.