Fernando Alonso says the Barcelona test is like the start of the pre-season for McLaren after the difficulties it had at Jerez earlier this month.
The Woking-based team completed very little running in the opening test of 2015, and Jenson Button was hit by trouble again yesterday.
Alonso had the best day of the pre-season so far today, covering nearly 60 laps in the Honda-powered car.
"There are is a lot of aero data to take, because we missed nearly the whole Jerez test, so for us this is like the first test for us," Alonso told reporters.
"There are many other teams that are quicker than us at the moment, but the feeling is good so that's positive.
"Every lap we do we learn things, so we are in a very early phase in the development of the car. It's very interesting and very challenging for all of us."
The two-time champion was nonetheless encouraged by the progress made so far, labelling his day as "beautiful".
"It has been a beautiful day for me, driving the car and exploiting some of the potential," he said. "The car felt better than at Jerez.
"Every lap is a learning process and I think we are enjoying this, but obviously we are halfway through testing and we need to make some progress, because we are happy with today, but we know we did 60 laps, the lower number of all the teams today.
"Still a long way to go, but we are making progress."
Australian GP not in June
"Same as Red Bull last year," he said. "We will arrive in Australia hoping that it was in June or July, but it's not, it's in March.
"I don't know if we will arrive completely ready, but what I'm sure is we will arrive in the best conditions we can, because everybody is working day and night to achieve that.
"I expected somehow to have this progress, because there are only six days of testing between now and Australia, so it's time to raise our game and to start putting in some laps and to start learning about the car. That was the aim.
"Today finally we showed that we are in the right direction. The potential of the car is there."