In an abandoned Norwegian mine last year, an unusual experiment produced results that drew scrutiny in boardrooms and government offices across Europe and helped to spark new regulations pouring fuel on already fiery EU-China relations. Ruter, the public transport authority for greater Oslo, drove new and used electric buses made by Chinese manufacturing conglomerate Yutong into a decommissioned mineshaft inside a mountain. There, cybersecurity tests revealed that the buses could be remotely...