This is a rapidly changing landscape - the data link you posted says it's for data posted ~20 Mar.
In my post above some more recent data (MARCH 23) shows Spain has now done more tests than Korea, and one province of China, Italy and the US have done almost a many total tests.
[EDIT] ON USA has also overtaken Korea in total number of tests
More important than the total number of tests is the number of tests per capita.
11 countries and 4 major regions have more per capita tests than Korea, and Australia has performed about the same number of test per capita as Korea.
The difference is Korea did many of their tests very early in the epidemic and used extensive tracking and tracing and quarantine more effectively than other countries.
Only 4 countries have tested more than 1% of their population for COVID19 and Korea is not one of them. While the signs from Korea are positive until more general testing is performed we wont know how far COVID has spread in any country.A blood test for COVID19 antibodies that uses a small amount of blood collected for all "routine" blood testing purposes is going to ultimately be useful to determine infection rates especially for non-symptomatic cases. This cannot be performed ON or even in a few weeks but will take many months so it won't help us in the near future.