We've not seen the back of him yet - Barcelona will offer definite evidence of exactly how strong Sebastian Vettel and Red Bulls title defences are. Photo by Mark Thompson/Getty Images

It’s the circuit that has come to signal the true beginning of Formula One’s championship battle. The stiff aerodynamic test that separates the grid two by two, as team-mates race each other with an extra edge over most weekends.

A track that has acted as a gateway to the European season, and a bellwether to who has the genuine pace and reliability to take the end of season silverware.

After four fabulous, unpredictable and enthralling races, things get serious from here on in.

It’s Barcelona this weekend and a Circuit de Catalunya that exposes any flaw your Formula One challenger may have hidden so far.

The big question is, what has everyone learned since that long and controversial weekend in Bahrain three weeks ago?

Well for starters, Lotus continue to look quick. Three days of testing at the Ferrari-owned Mugello circuit last week reaffirmed that.

With the development race well and truly on, it may be those at Maranello can turn a tough start for the F2012 into a real contender sooner than most could have imagined.

But with McLaren’s progress stalling and Mercedes remaining unpredictable, now could be the perfect time for the Norfolk marque to strike.

And ex-Lotus driver Johnny Herbert agrees: “Lotus seem to have a car – and the drivers and maybe engineers – to have a little bit of understanding about how to get the car in that window (to optimise the tyres).

“They have shown speed all the way through the season so far. It just clicked together properly in Bahrain. And so, I think yes (they can win at Barcelona) and from what we saw in Mugello I think they can move forward in a positive way.

“The guys that probably have been most consistent this season, strangely enough, are Lotus.”

Clearly some teams we want to see learn – others, maybe not.

Red Bull have been the masters of the F1 grid for some time, but it’s hard to imagine a bigger turn-off for some fans than seeing Sebastian Vettel running off into the distance from pole in Barcelona.

It wasn’t quite that easy at Sakhir, but the nett result was familiar.

And that is why it will feel like the season is starting all over again this weekend. From FP1 to Q3, we are about to find out who – if any – really has the form for a season-long fight.

• It says something when a team principal hopes a whole test is rained off – that’s what Lotus team principal Eric Boullier wants to see in July.

A record 20-race calendar means the young drivers’ test, usually held at the end of the season in Abu Dhabi, will be split between there and a second venue. Silverstone is the proposed partner, with the test to take place immediately after the British Grand Prix in July.

But that isn’t sitting well with a bullish Boullier: “I’m a supporter of young drivers, and for me Abu Dhabi was the perfect scenario,” he told Autosport.

“The young kids finish the season, and you can organise this test in a hot, nice place, with nice variety. So I was actually a bit cross with the decision to bring it earlier to Silverstone. For me it is absolutely a nonsense to have the test in July when all the young kids are in the middle of the season and focused on racing and the championship.

“I obviously have to choose what is best (financially) and that is Silverstone. But actually I would like it to rain, so we will go back to the original schedule – which for me is the normal one.”

Red Bull and Toro Rosso are the only two teams to opt for a November date after the Abu Dhabi Grand Prix.

• It was good to see the different reactions to Mugello.

First was Vitaly Petrov – a new generation, a racer learning his trade.

The Russian’s view was clear – the track was too narrow, too dangerous. And then there was hardened racer Mark Webber.

He tweeted: “Did 10 dry laps today around Mugello, which is the same as doing 1,000 laps around Abu Dhabi track in terms of satisfaction. #realtracks #fast.”

Sometimes you just can’t help being a Webber fan.

• It is still far from over, but Caterham have at least scored another – albeit small – win over Force India in their long running copyright court case.

The issue stems back to when Caterham designed its first car for 2010, contracting in Aerolab’s facilities to help.

The Italian company fell out with Force India over being paid for its services, and was found to have used some of its knowledge from working for Vijay Mallya’s outfit in the design of Lotus Racing’s T127

Force India won £20,000 in damages, but were ordered to pay the £700,000 it owed Aerolabs for the original work. And last week the Silverstone team was told to pay another £650,000 to Caterham technical chief Mike Gascoyne.

But this will continue to run. Force India plan to put in an appeal against the findings when allowed, while they will no doubt continue to argue for the FIA to sanction the Norfolk team over a 2010 ‘advantage’. The end is far from in sight.