We don't have the capacity to test everyone. No one does, but evidently South Korea and Germany are a lot closer to achieving that than other countries have.
In the chart by country here
Coronavirus Update (Live): 139,485 Cases and 5,120 Deaths from COVID-19 Virus Outbreak - Worldometer look for the countries with the smallest proportions of deaths relative to total cases ... that's probably because they're identifying more cases.
China about 4% (their situation is understandable given that this is where the situation started) - Compare the number of active cases to the number recovered - their number of active cases is dropping by 1000 - 2000 per day, they will be over this soon.
Italy about 6% (their health care system was, and is, overwhelmed by too many simultaneous cases)
Iran about 5% (don't know how good their health care system is)
South Korea about 1% (they have done very aggressive testing to identify cases and isolate them early as much as possible) - Daily new cases peaked more than a week ago. They are over the hump.
Spain about 3% (number of cases is escalating rapidly - I'm in the process of postponing a planned vacation there by several months)
Germany about 0.2% (!) (very aggressive testing to identify cases early - the Germans are being German)
France about 2%
USA something over 2% (but it's early)
All the others have too few cases to be meaningful.