Watson is a classic populist idiot. Most of the "closed border" countries don't test much if at all. Does he think random towns somewhere in Russia actually have Covid testing kits? Russia's own doctors said they suddenly have many thousands of sudden new pneumonia cases in the last few weeks, "coincidentally" when Covid is roaming around. No-one gets tested. If you close your eyes, you see no problem. He should move to North Korea, it's his ideal country.
Countries have to have borders. If closing the border is not effective why liberal countries like Canada, etc are closing their borders now?
Countries need borders if there's good reasons to have borders. With most European countries, there's no reason to have borders during normal circumstances. Countries are now closing borders because they don't want to overwhelm the medical system. They need to control the rate of spread. Unless you will isolate your country completely, border checks don't work. People can carry it in without any symptoms.