If you had an instant test with a very low false negative rate, and in quantities such that you could test every traveler, then there would be no reason to ban travel because you have created a situation where the virus cannot move, but using tests instead of banning human travel.
My impression is that you could do something almost as good with well-managed quarantine that lasted long enough for you to be sure about the test results.
Most travel is not worth the hassle of a 7-14-day quarantine though
It depends on the test.
If you had an instant test with a very low false negative rate, and in quantities such that you could test every traveler, then there would be no reason to ban travel because you have created a situation where the virus cannot move, but using tests instead of banning human travel.
My impression is that you could do something almost as good with well-managed quarantine that lasted long enough for you to be sure about the test results.
Most travel is not worth the hassle of a 7-14-day quarantine though