Yes, you do need a test to enter the United States when you fly from Fiji.

On January 12, 2021, CDC issued an Order requiring all air passengers arriving to the US from a foreign country to get tested no more than 3 days before their flight departs and to present the negative result or documentation of having recovered from COVID-19 to the airline before boarding the flight. This Order will go into effect at 12:01am EST (5:01am GMT) on January 26, 2021

This Order applies to all air passengers, 2 years of age or older, traveling into the US, including US citizens and legal permanent residents.

Source: https://www.cdc.gov/coronavirus/2019-ncov/travelers/testing-international-air-travelers.html

You currently do not need to quarantine on entry to the United States providing you fly directly from Fiji. However, you should continue to take steps to protect others from getting sick. Wear a mask when outside your home, stay at least 6 feet from people who are not from your household, wash your hands often or use hand sanitizer, and watch your health for signs of illness.

Source: https://wwwnc.cdc.gov/travel/notices/covid-1/coronavirus-fiji

You currently do not need to self isolate on entry to the United States providing you fly directly from Fiji.

You should continue to take steps to protect others from getting sick. Wear a mask when outside your home, stay at least 6 feet from people who are not from your household, wash your hands often or use hand sanitizer, and watch your health for signs of illness.

If you participated in higher-risk activitiesget tested 3–5 days after travel AND stay home for 7 days after travel.

Source: https://wwwnc.cdc.gov/travel/notices/covid-1/coronavirus-fiji

For more information on keeping safe after your vacation, visit https://www.cdc.gov/coronavirus/2019-ncov/travelers/after-travel-precautions.html