LONDON—Britain is planning to test a series of measures including “coronavirus status certifications” over the coming weeks to see if they can allow people to safely return to mass gatherings at sports arenas, nightclubs and concerts. People attending a range of events this month and in May, including a club night and key FA Cup soccer matches, will need to be tested both before and after. The trials will also gather evidence on how ventilation and different approaches to social distancing could enable large events to go ahead. Officials are also developing plans to test out COVID-19 passports that are expected to show if a person has received a vaccine, has recently tested negative for the virus, or has some immunity due to having had coronavirus in the previous six months. The issue of vaccine passports has been a hotly debated topic around the world, including in the United States …