But debate about whether it was private or secret, just how many kilometres the team did on 2013 rubber, and why its drivers ran in unbranded helmets will become largely irrelevant on Thursday.
Instead, when the FIA's International Tribunal opens for session at 9:30 local time in Paris, Mercedes team principal Ross Brawn and Pirelli motorsport director Paul Hembery will be cross-examined to find out simply whether or not the rules have been breached.
The Mercedes test case revolves around a three-day 1000 kilometre tyre test that the team did for Pirelli with its 2013 car in the week after the Spanish Grand Prix.
F1's Sporting Regulations appears to be fairly clear in defining that such running of a current design is not allowed.
Article 22.1 states: "Track testing shall be considered any track running time not part of an Event undertaken by a competitor entered in the Championship, using cars which conform substantially with the current Formula One Technical Regulations in addition to those from the previous or subsequent year."
It furthermore clarifies that no track testing can take place in a period that spans 10 days before the start of the first race of the season and December 31.
The only exception is the young driver test, four one-day aerodynamic tests at straight line or constant radius sites, or in cases where a replacement driver needs some emergency mileage to get up to speed.
While it appears that Mercedes' running of its W04 is a straightforward breach of the rules, the matter is complicated by clauses in the supplier contract that Pirelli has with the FIA.
In it, Pirelli is allowed to conduct 1000 kilometre tests with current teams using a 'representative' car.
Although it is believed that there is no strict definition of what a representative car is, equally there is nothing that states a representative car cannot be from the current campaign.
The crux of Mercedes' defence will therefore revolve around whether or not Pirelli's right to run a representative car in its three-year old contract supersedes what is stated in the current Sporting Regulations.
Mercedes will certainly have sought permission from the FIA about running a 2013 car - and would not have been brazen enough to take a chance on such an obvious breach of the rules if it did not believe it was allowed to do so.
But believing you are within the rules, and actually being within them, are two completely separate things. For even if you do not intend to break the rules, that does not stop you being punished if you are found guilty of breaking them.
The International Tribunal has already received written submissions from Mercedes, Pirelli and the FIA over the matter.
Its mandate to work out whether or not the rules were broken will revolve around the correspondence between the three interested parties - and questioning of the main parties in the Paris hearing.
What took place at the test is of little consequence, for it is the simple use of the 2013 car itself - not what it did – that really matters.
Predicting how deep the investigation needs to delve into the lines of communication between Mercedes, Pirelli and the FIA will ultimately depend on just how much debate there was about using a 2013 car, and how clear each party was about the others' intentions.
Was, for example, any FIA approval on the basis that every other team had been offered such a test, so in theory unanimous support was forthcoming for a future rule change?
Or was it explicit that the FIA's legal interpretation was Pirelli's contract supersedes the rules, so there was no question that running a 2013 car was allowed?
Then, once the FIA's stance has been clarified, the IT will need to look at whether Mercedes' use of a 2013 was a blatant bid to cheat – as some of its rivals have all but suggested – or simply an unwilling transgression made in good faith.
Only then can a ruling be made on what - if any - punishment should be handed down.