This is from the HAL web site.
Guests ages two and above will require a medically observed, negative viral COVID-19 test (PCR or antigen) result taken within three days of cruise embarkation for all European cruises unless embarking in Greece. All cruises embarking in Greece require a medically observed, negative viral COVID-19 test (PCR or antigen) result taken within one day** of cruise embarkation.
If a guest brings proof of testing without results to the pier, Holland America Line will test them at no charge. Guests who arrive without a negative test result will experience additional fees, a delayed embarkation and risk denied boarding and subject to quarantine should a positive result be returned.
**For guests embarking in Athens, Greece, we understand that a one-day medically observed COVID-19 test may not be possible based on the timing of your arrival to Athens. For your convenience we are currently offering complimentary antigen testing at the terminal. However, Holland America Line strongly recommends guests take a medically observed viral COVID-19 test (PCR or antigen) prior to leaving home to avoid queues and travel disruptions associated with a possible positive result on the day of embarkation.