Fernando Alonso said he has no intention of leaving McLaren or Formula 1 before his contract ends in 2017.
His future has been the subject of speculation after McLaren boss Ron Dennis said last November that they had discussed the idea of a sabbatical.
After his first test in the new McLaren, Alonso said he would "of course" see the season out, adding: "And the next one.
"I have a contract for three years. I'm not thinking about anything else."
He added: "This is a very important year for us."
The 34-year-old two-time champion, who is still regarded by many as the best driver in F1, indicated on Tuesday his wish for McLaren - and Honda - to turn their performance around after a difficult 2015 in which they finished ninth out of 10 teams.
"The ambition is very high," he said. "I am not here just to travel around the world and to jump in the car and have some fun on Sunday. I am here to win."
At the end of 2014 Alonso quit Ferrari because he believed McLaren offered him a better chance of winning a third world title. Ferrari's lead driver Sebastian Vettel was fastest for the second day running on Tuesday during pre-season testing in Barcelona.
Alonso ended his first day in the 2016 car eighth fastest, 3.2 seconds off the pace, but 0.7secs quicker than team-mate Jenson Button had been on Monday.
The McLaren ran reliably - Alonso did the equivalent of a race distance in the morning session and managed well over 100 laps for the day.
Honda, which announced a new head of its F1 programme on Tuesday, has, according to Button, fixed one of the biggest issues with its engine - its weakness in deploying recovered electrical energy.
However, the engine is still believed to be a significant margin - perhaps as much as 100bhp - down on the standard-setting Mercedes in terms of absolute performance.
Honda has a new engine for next week's second and final test.
Alonso said McLaren-Honda needed to "improve all areas of the car" but said he believed the team could have the best chassis by the start of the European races in May.
However, he said he believed Mercedes' domination of F1 "had not finished".
Testing day two - who was fastest and what does it mean?
Vettel set the pace 0.715 seconds quicker than Red Bull's Daniel Ricciardo, as both drivers became the first to use the new ultra-soft tyre introduced for slow tracks this year.
Force India's Sergio Perez was third fastest on the super-soft tyre and Mercedes' Nico Rosberg fourth on the medium tyre.
Rosberg was two seconds off Vettel but Mercedes had an impressive day.
Don't believe the times
Rosberg completed more laps than anyone else - as did team-mate Lewis Hamilton on the first day of the test on Monday - and taking into account the differences between the tyres, world champions Mercedes still appear to have a very strong car.
The ultra-soft tyre is designed for low-grip slow tracks, not Barcelona, where the long corners and abrasive surfaces are hard on tyres. But it is much softer and would provide better grip and therefore greater speed over a short distance.
Tyre supplier Pirelli estimates the lap-time difference between the ultra-soft and the medium at 1.8-2.3secs, based on initial data.
Pirelli also said it believed the difference between the medium and super-soft was about 1.4-1.5secs - and Rosberg was only 1.2secs slower on medium tyres than Vettel's best time on the super-softs.
On the face of it, that might suggest Mercedes still had a small advantage over Ferrari.
However, the times are not necessarily directly comparable - even taking the tyres into account - because the teams do not reveal the fuel loads the cars are carrying - and 10kg of fuel is equivalent to nearly 0.4secs a lap at Barcelona.
|Barcelona testing: day two - final times|
|Sebastian Vettel (Ger)||Ferrari||1:22.810|
|Daniel Ricciardo (Aus)||Red Bull||1:23.525|
|Sergio Perez (Mex)||Force India||1:23.650|
|Nico Rosberg (Ger)||Mercedes||1:24.867|
|Marcus Ericsson (Swe)||Sauber*||1:25.237|
|Esteban Gutierrez (Mex)||Haas||1:25.524|
|Valtteri Bottas (Fin)||Williams||1:25.872|
|Pascal Wehrlein (Ger)||Manor||1:25.925|
|Fernando Alonso (Spa)||McLaren||1:26.082|
|Jolyon Palmer (GB)||Renault||1:26.189|
|Max Verstappen (Ned)||Toro Rosso||1:26.539|
|* 2015 carVettel and Ricciardo set best times on the ultra-soft tyre; Perez on the super-soft; Ericsson, Bottas, Gutierrez, Wehrlein, Alonso and Palmer on the soft; all others on medium.|
What can be said is that the Mercedes ran reliably and produced consistently impressive lap times over all its runs. Rosberg ran a remarkable 172 laps to add to the 156 done by Hamilton on Monday.
Vettel said he was "fairly happy" with the performance of the Ferrari - which is a much more radical design departure from last year's car than the Mercedes.
However, Ferrari are the ones with all the work to do - Mercedes had an average advantage of 0.6secs a lap in qualifying last year.
Vettel brought the session to a slightly premature end when his car stopped out on track with five minutes to go, causing a red flag.
Among the rest of the field, the new Haas team impressed, with Mexican Esteban Gutierrez setting the sixth fastest time after a delayed start because the car needed its front wing strengthened after a failure on Monday.