One useful "sanity check" for countries under testing is to check the records of imported cases from countries doing rigorous contact tracing and publishing the

One useful "sanity check" for countries under testing is to check the records of imported cases from countries doing rigorous contact tracing and publishing their data. So far, Singapore has 2 confirmed cases arising from Japanese travellers and Taiwan has 1: https://www.againstcovid19.com/singapore/dashboard https://www.againstcovid19.com/singapore/dashboard https://www.againstcovid19.com/taiwan/dashboard https://www.againstcovid19.com/taiwan/dashboard This is vs the ~110 British cases and ~50 American cases the two countries have seen collectively. Flight volume from Japan to both countries is normally quite substantial so this is evidence to suggest that Japan's case is not low solely due to undertesting.