With a very limited amount of testing allowed in F1, this track time is absolutely vital!
Aside from race weekends, it's very rare to see the current generation of Formula One cars out on track. This is because teams are restricted in the number of times they can run their latest creations.
The test events and the number of days is the same for every team, and each is allowed two promotional events (filming days capped to a maximum distance of 100km each) and two demonstration events (with a maximum distance of 15km) per season.
This season, there have been two in-season tests, where teams can run one car each. This car is often a different chassis to those that race every other weekend, but sometimes the race cars are used at the tests. The engine and gearboxes are test items, though, and don't come from the pool for the season.
The first in-season test was after the Bahrain Grand Prix, with two days of running in the Sakhir desert, and the second is taking place on the Tuesday and Wednesday after the Spanish Grand Prix.
Tests run from 9am to 6pm with a one-hour lunch break from 1pm to 2pm in between, although these timings can occasionally change depending on the circuit. They're also open to negotiation if wet weather or incidents create lengthy delays or loss of track time.
The main reason for going testing is to find performance. One of the most important elements of this is information gathering - hence why you'll often see cars running a variety of different sensors, aero rakes and other devices. Every run a car does, the team gets back a huge amount of data that can be delved into during the test or afterwards, to find out how new parts, set-up changes or the tyres have reacted and performed.
It's not about tuning the car to the specific circuit. These tests provide chances to answer more fundamental questions for moving through the season - directions to take, routes to go down. Runs can vary from looking into how tyres degrade over a stint, to how new the airflow around the car changes when new aero parts are added.
Just like every session over a race weekend, teams go into these sessions with detailed run plans, in order to try and maximise the track time and investigate performance on every aspect of the car. Not everything can be changed at once on an F1 car, otherwise it becomes hard to really analyse and get results from the data.
Instead, teams need a structured programme, so each new item or change has a run to compare against. That way, teams can see if the comparison is good, bad or indifferent, and can then progress forward with whether to go down that route or not.
Testing is an opportunity to focus on broader, bigger picture changes to the car. There's so little time on a race weekend, practice is mainly focused on the details - qualifying balance, energy deployments, single lap pace, race set-up, engine cooling, tyre windows. Those are just a few examples...
There isn't much opportunity to conduct deeper investigations over a race weekend and that's where testing becomes vital. It's also a chance to re-correlate simulations to the data and information you collect over the test. Windows to do that don't come around very often during a season.
The Circuit de Barcelona-Catalunya is just the kind of track you want to test on, and that's why it's the winter testing venue year after year. It contains every kind of corner you could want, from high speed sections to low-speed hairpins. This makes it a challenging and demanding track for a Formula One car, putting it through its paces.
F1 regulations require teams to split their in-season test running, with two days reserved for young drivers - as a way of providing up and coming racers with the opportunity to gain experience behind the wheel of F1 machinery and showcase their talents.
A young driver is classed as someone who has competed in fewer than two Grands Prix. It's an important aspect of the regulations for the next generation of stars, but it does mean the race drivers have fewer days behind the wheel of the car - and they're the ones who know the cars best and will provide the most accurate feedback.
Bad weather can impact track time for teams, but that's the same for everyone. Getting struck down by a reliability problem or a broken part is an issue that will only impact the team involved, and this can have a big impact on not only the test itself but also the season as a whole.
That's because testing is so limited and opportunities to run the cars outside race weekends are so rare. The development race in F1 is incredibly fast-paced and constantly moving forward. Every team is pushing to the absolute maximum at every opportunity.
Lose time during an in-season test and suddenly that team is standing still, while everyone else moves forward. The work done during the tests will remain for the lifespan of the car and potentially into future seasons, too. So, racking up the mileage is absolutely crucial.