Foreign travelers over six years old must have a medical certificate, issued within 72 hours before the border crossing date, indicating a negative COVID-19 test result. The requirement does not apply to citizens with temporary or permanent residency permits.
Children under the age of 2 are exempt from presenting a COVID-19 test.
Travelers with proof of recovery from the virus within the last 90 days prior to boarding. Proof of a recent positive viral test and a letter from your healthcare provider or a public health official stating that you were cleared to travel.
More info at the CDC site
Travelers who did not get tested, are advised to stay home and self-quarantine for 10 days after travel.