Former world champions Lewis Hamilton and Fernando Alonso will be on track in the next two days after Mercedes and Aston Martin sent their drivers to Jerez for testing.
The exercise is on behalf of tyre manufacturer Pirelli as they look to evaluate compounds.
Hamilton and Alonso will be accompanied by team-mates George Russell and Lance Stroll as they seek to put in over 100 laps each on the Spanish circuit, per Spanish outlet Marca.
The reps on track, which are expected to be in last year's cars, will be valuable for the teams and drivers as much as the tyre manufacturer as Alonso seeks to continue to acclimate to his new team and the Mercedes pairing seek to get up to speed as they look challenge at the front of the grid more often this coming season.
Memories for Alonso
It's a behind-closed-doors test and there will be no official timekeeping, only what is shared between Pirelli and F1.
The trip to Andalusia should evoke some memories for 2005 and 2006 world champion Alonso in particular, who did his first laps in a Formula 1 car there for Minardi at the end of the previous century.
That December '99 test was the first foray into F1 for the Spaniard – who would've known then that he'd go on to be the most experienced Formula 1 driver of all-time?