The first week of Formula 1 testing is in the books and, as you would expect, there are more questions than answers as to what lies ahead in 2019.

Some teams appear to be off to a strong and competitive start, while others flattered to deceive in Barcelona, so what can we take away from the first four days of action?

Here are some early observations which you may or may not take with a pinch of salt!

1. Ferrari off to a flyer

Perhaps the only conclusion that can be made with a degree of certainty is that Ferrari does appear very well placed heading into the new season.

From Monday morning the SF90 was at the top of the timesheets and while we have seen the Scuderia do this before, you'll be hard-pressed not to find someone who doesn't think their pace wasn't genuine.

Charles Leclerc and Sebastian Vettel both set their best times of the week using the C3 tyre, the middle compound of the five Pirelli has produced.

Yet they only sit seven-tenths off the fastest time of the week, set by Nico Hulkenberg in the Renault on the softest C5 rubber, which the Italian supplier believes should be 1.2 seconds per lap faster.

It's not like the fastest laps both drivers conducted appeared to be glory runs either.

So with an apparent 0.5s advantage over Renault just from the tyre and with plenty more performance to come is an ominous warning, particularly given the French manufacturer is expected to be the fourth best team.

That performance was also matched by seemingly bulletproof reliability as Ferrari completed just 12 laps less than Mercedes, and they were swapping drivers every day too.

A final note must also go to Leclerc who was completely unphased by his task at hand and was more than capable of keeping up with Vettel in every area.

2. Red Bull-Honda will be a force to reckon with

Ever since it was confirmed Red Bull would be changing to Honda engines for 2019, there have been some refusing to consider the idea the partnership might just work.

However, after Week 1, those doubters should already be pinching themselves after four days of undramatic running which had to be seen to be believed.

It's more than likely that the engine was in a very conservative mode and we don't know if the same unit did all four days, but compared to their expected rivals, Red Bull certainly don't appear to have any major deficits.

The team never reveals their hand in the first week, so to end the test only 0.7s off a Ferrari receiving many plaudits on the same tyre is a very good base from which to start.

Of course, Red Bull has talked up their expectations at every opportunity, but even they will concede most of their ambitions are targeted for the second half of the season.

But, based on the first impression, there's no reason at all why they won't be regular race winners in 2019, particularly with Max Verstappen appearing more focused and more hungry than ever before.

3. Mercedes DO have work to do

Mercedes did Mercedes to an absolute tee in the first test, focusing predominantly on long runs with a car that ran like clockwork.

However, unlike previous years this wasn't a German manufacturer that you knew was simply keeping it all under wraps because something did seem off.

Maybe, it was because Ferrari was doing what the same while also looking fast but even when Lewis Hamilton and Valtteri Bottas did pick it up on Thursday they hardly left anyone in awe.

Are they slow? Of course not. We all know come Australia the fuel will come out, they'll find the magic power buttons and suddenly be competitive.

But they were struggling with the tyres in cold conditions, as highlighted by their inability to find much lap time with the C4 and C5 compounds, and there was just no reason to think somehow they have pace that Ferrari and Red Bull can't match.

4. The midfield is closing the gap

It does appear likely that the top three teams will remain in their private battle at the front, but the midfield may well be in 'F1.25' compared to 'F1.5' to use the analogy suggested last year.

Renault was able to keep in touch with what the top teams were doing but there's no indication yet they will make it a 'big four'.

Hulkenberg's best time on the final day was solid enough but the car failure soon after highlighted why reliability remains an issue and it won't go down well to see the Honda engine complete more laps over the first test.

With strong pace and reliability, Alfa Romeo and Toro Rosso do look capable of keeping up with the French manufacturer, as will Haas when they overcome the reliability niggles and start using the softer tyre compounds next week.

5. The curious cases of McLaren and Racing Point

McLaren promised they had worked on reliability for testing and that was the case as they managed 445 laps, much higher than the figures of recent years.

However, performance does seem lacking with their best time of 1m18.4s on the C4 tyre, 1.1 seconds slower than Hulkenberg's benchmark on C5.

So while it would appear they have made some progress, it will be interesting to see where that puts them in the eventual competitive order.

As for Racing Point, they disappointed with lap times well off the pace set by their expected midfield rivals and a lack of running with just 248 laps to their name.

2019 is thought to be a building year for the team in their new guise and financial position, but even so, a greater impact was still expected.

6. Williams at rock bottom

Where to start with Williams... It was thought last year's disaster couldn't get worse yet, three weeks before the start of the new season, it seems that might be the case.

Having missed the first two-and-a-half days, the new car finally got on track meaning, hopefully, they can now focus on catching up but it really doesn't bode well for their competitiveness.

The question I have is how could Williams have gotten it so wrong? Given their struggles last year, they could have switched focus to 2019 far earlier than most and put themselves in a good position to make progress.

Instead, we have deputy boss Claire Williams suggesting they have only now learnt their car build plan isn't "fit for purpose".

The only feasible reasons for the delays are either financial, or the team hasn't learnt the lessons of last year which would be even worse.

They can put a brave face on publicly, but behind the scenes, Robert Kubica and George Russell must be wondering what they've let themselves in for.