The panel at the International Tribunal has adjurned until tomorrow after all parties in the 'testgate' scandal put their cases forward.
Meeting in Paris representatives from Mercedes, Pirelli and the FIA argued their case as representatives from other teams watched on.
First in the dock was the FIA and a lawyer for the governing body was quick to criticise Mercedes.
"Any running on the track is deemed to be testing," the FIA's lawyer said.
"It is difficult to say that Mercedes gained no benefit," he added.
The FIA's argument continued describing the way Pirelli and Mercedes went about obtaining permission for the test as "very odd".
It is believed Mercedes and Pirelli made "informal" telephone and email communication with race director Charlie Whiting and a FIA legal representative.
Mercedes and Pirelli went ahead with the test without receiving a definitive response was another claim made the governing body.
Next came Mercedes who countered the FIA's claims by saying the test was not undertaken by the team, it was instead a test undertaken by Pirelli and as a result does not break the rule banning in-season testing.
One slightly confusing angle of Mercedes' argument was the team implying Ferrari is liable for committing the same offence after the Scuderia took part in a separate Pirelli test in Bahrain with it's 2011 car just weeks before Mercedes did in Barcelona.
This was confusing as it does imply Mercedes believe they are guilty of breaking the regulations themselves but also feel Ferrari are as well.
What Mercedes did agree on however was the decision to tell it's drivers Lewis Hamilton and Nico Rosberg to wear black helmets, telling the court it was "regrettable".
"We acknowledge this aspect was bound to raise suspicion," he acknowledged.
Pirelli's testimony closed the proceedings and the Italian tyre supplier came out very strongly insisting no rules or contracts had been broken by completing the test and also claiming they could not be punished by the court as they are not a driver or a team.
A decision is expected today.
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