Did testing help South Korea contain this virus or not?
South Korean has been at about 8000 for a while now... Italy and Iran not so much.
Too late for that now. You can blame the Obama administration, lifer-congress critters, and lifer Federal bureaucrats for failing to reform regulations and processes after the MERS outbreak -- that is what South Korea did. It was no magic that they were better prepared than most countries. They made the necessary changes years ago.
Bogging down the Trump Administration with constant hoaxes and impeachment garbage probably didn't help us either.
Testing can be for surveillance or diagnostics. Surveillance testing is aimed at reducing the spread of infection or monitoring the spread of infection. Diagnostic testing is to identify infection for treatment purposes.
The treatment for covid-19 is self-isolation unless severe symptoms develop. The same as the FLU, you don't need a test to figure out what to do.
Note, I am not suggesting that Covid-19 is "just the flu." I am suggesting that the treatment and preventative measures are the same as for the flu, until a cure or other treatments are discovered.