Many countries and airlines require you to provide evidence of a negative COVID-19 (PCR or RAT) test in the days prior to travelling. Governments determine the testing window within which you need to comply. 48 Hours prior to departure is relatively standard, however some countries allow testing within 72 hours of departure.
Some countries also require IgM antibody screening prior to departure. An IgM antibodies test detects the SARS-Cov-2 virus that causes COVID-19. When IgM is detected you may still be infected, or you may have recently recovered from a COVID-19 infection.
Rapid Antigen Testing may also be used by governments on arrival, when transiting, or post arrival at your destination, such as in Fiji. It is important to understand all of the testing requirements for the destination you are traveling to and through.
A good tip is to ensure you have a printed and digital copy of your results with you as you travel that you can access offline if required.