I can verify this is true, Vietnam did very few testing. If anything aside from a few wealthy countries, most others don't have the resource to do it on large scale anyway. But geographically it has some advantages going for it. First most countries are homogeneous so immigration traffic is almost non-existent. Secondly the borders are often stricter. It means new vectors are fairly limited in number, and those few that exist there are met with a hammer - i.e when the first couple cases detected in a town near China border, the government immediately shut down the border and put the whole town (with ~10000 people) in quarantine overnight.
While they can be considered "good example", I'm not sure the lesson is really applicable for Western countries though. Your borders are much more boros, and the people here won't stand for the hammer approach. Limited testing works before you start having community spread. Once you do, either you have to test a lot to keep track of progression and slow down further spread, or stop and brace yourself in hope of herd immunity (kinda like what the UK government originally tried to do).