Testing is only part of it. Korea never mass tested the population at large. They traced the chains of the infections and quarantined everyone until they were

Testing is only part of it. Korea never mass tested the population at large. They traced the chains of the infections and quarantined everyone until they were tested clean. They found new chains through sick people who were tested. Without investigation and tracing the chain of infections, you can't contain it through testing alone. And the fact that were was an undetected outbreak in the west coast of the United States for several weeks probably made containment impossible, even using the South Korean model.