Former City Administrator Jestin Johnson testified Thursday that former Mayor Sheng Thao asked him to visit a modular-housing company at the center of her federal corruption trial but never instructed him to purchase its units or bypass the city’s competitive bidding process. Federal prosecutors allege Thao agreed to help Evolutionary Homes, a business associated with California Waste Solutions executives David and Andy Duong in exchange for political benefits and payments to her longtime partner, Andre Jones. Thursday’s testimony explored how…