Reliability issues continue to hamper development, but drivers seem happy with MP4-30.
McLaren racing director Eric Boullier has admitted that the development plan of its 2015 Honda-powered Formula One car is '50 percent behind' where he planned it would be.
At the halfway point of pre-season testing, teething problems with Honda's brand new V6 power unit and hybrid ancillaries has seriously affected its capability to run for anything other than a few laps at a time.
"We did maybe 50 percent of what we wanted to do," said Boullier of the testing programme so far.
"We have 12 days to get ready, so if we miss half then we won't be ready 100 per cent. So our development – in terms of plan – we are 50 percent behind."
Despite the reliability issues on the engine side, the new McLaren chassis appears to be a step forward from last year's recalcitrant machine.
"It's early days, but what I can say is the car is behaving or handling differently from last year's car, and the drivers look happier," said Boullier.
"Especially Jenson, who knows the car obviously, and even Fernando doesn't look unhappy with the car, which means it's not bad. We just started today to compare different airflows."
Car lasts for 59 laps
Today's running with Alonso behind the wheel was the most encouraging yet, and basic setup work was performed today as the car ran for longer than ever before.
"We are not obviously looking for performance," said Boullier. "The expectation of what we wanted to build, it looks like we achieved it so far. Next week there should be some more parts.
"We have a lot of systems to check, that includes a lot parameters to understand the car. We have to do a lot of mileage, to gather data, before we concentrate on performance. The priority is the development programme.
"The car is still in launch configuration. We couldn't put enough miles now to bring some more parts.
"Next week we'll see another step, and then in Australia we'll see another big step.