With the first of 2016's Pre-Season Test sessions now under our collective belts, RaceDepartment takes a look at a few things we learned, and didn't learn, over the course of the first four days of F1 action this year. Mercedes look pretty much bulletproof It feels an awful long time since reliability hasn't dominated the F1 news since the adoption of the now not-so-new V6 Turbo engines, but reliability for all teams across the board in Barcelona has been fairly impressive. Even newcomers Haas, minus a front wing failure on the opening day, have been able to run with few problems. But one team, as per usual by now, certainly stole the show. Put aside the fact that Mercedes' car once again looks formidably fast, it seems the reigning world champions have unlocked the secrets to seemingly nigh on bulletproof reliability. To put things into perspective, the Brackley outfit managed to put over 100 laps on the board on all four days, and even had to split driving duties on a morning and afternoon basis between Hamilton and Rosberg due to fears that they wouldn't 'be fresh' come Melbourne. As a final 'embarrassment' to the rest of the field, Mercedes managed to complete 800km of testing on the final day alone, or, in other words, they covered more distance in a single day then they would complete over an entire Grand Prix weekend. Of course at this time the lap times themselves mean little. But reliability wise, Mercedes are definitely leading the way, and they have assured the outside world that not only is their car incredibly reliable, but it remains astonishingly quick too. Haas and Manor - The two dark horses for 2016 In many ways both Haas and Manor can be seen as direct rivals for the new season. After all, even after having competed in F1 in the best part of half a decade in different guises, with the introduction of their first completely new car since the start of the V6 Turbo era it wouldn't be too extreme to see Manor also as a brand new F1 team. With that in mind, both Haas and Manor have been surprisingly competent over the first four days of testing. First things first, both teams have proven to be pretty damn reliable, if we put aside Rio Haryanto's misdemeanors behind the wheel of the Manor. Whilst neither team managed to get near the mileage of the bigger outfits, for two new teams to have comfortably over 100 laps for each of their drivers, especially in an era almost defined by unreliability, is a great achievement. If we add to that, that Haas was able to complete a full race simulation on day four, the ominous 2014 pre-season test and the shambles that was the 2015 Australian Grand Prix seems an awfully long time ago. However, there are still things to do and problems to solve. Haas has already admitted that they have several things to fix on their car, namely how to keep their front wing from disintegrating at high speed, whilst Haryanto will need to find his rhythm quickly if he is to stack up favorably to the Mercedes backed Wehrlein. But with arguably the two strongest lineups two new teams have entered F1 with in a long time, the future seems bright for Haas and Manor. A McLaren revival or same old, same old? One of the biggest questions on every F1 fans lips prior to this was whether McLaren would be, frankly put, just as completely useless as they had been throughout 2015. Having endured their worst season since 1980, and, as a result, simply wiped off 2015 as a 'learning year', there can be absolutely no excuses for either McLaren, or Honda for that matter, not to get it right in 2016. Early signs seemed good for the former world champs with both drivers enjoying relatively good mileage on the opening days of the test, prompting Alonso to reveal that McLaren are aiming to have the best chassis in F1 by the start of the European season. However, the old gremlins seemed to wiggle their way back into the team with Alonso's running on the final day to just three installation laps thanks to a coolant leak in a tricky-to-reach area which prevented him from venturing out for the rest of the day. Regardless of Alonso's insistence that McLaren are the only team who can beat Mercedes in the foreseeable future, one does have to wonder where McLaren will stack up this year. After all, they don't have the convenience of two 2014-spec cars occupying the last row of the grid to save their embarrassment this time around. How do you see the 2016 season shaping up? Leave your thoughts in the comments below!