Drivers Jean-Karl Vernay and Alejandro Garcia completed two days of testing aboard the revived Isotta marque's Tipo 6 Competizione LMH at Estoril.
French outfit Duqueine will enter a single car in the 2024 WEC under the Isotta Fraschini Duqueine Team banner after the manufacturer's split with originally confirmed partner Vector Sport was announced last month.
Isotta motorsport boss Claudio Berro has acknowledged that the change of team had been made for financial reasons, with the LMP2 class regulars stepping up from the European Le Mans Series for a maiden WEC campaign.
Berro said: "I am very satisfied with the first test done by the Isotta Fraschini Duqueine team. It was also Alex Garcia's first time driving a hypercar and he behaved very professionally, assisted by Jean -Karl Vernay.
"The two Portuguese days saw several long runs in which the car performed perfectly, which allowed us to collect a lot of information on the tyres and on the set-up and aerodynamic settings."
Vernay, a Le Mans 24 Hours class winner in 2013 who most recently raced for Hyundai in the FIA ETCR - eTouring Car World Cup, and reigning ELMS LMP3 champion Garcia are the first two drivers confirmed to race the Isotta, which has been built by long-time Ferrari technical partner Michelotto and features a front-axle hybrid system.
Former Audi LMP1 racer Marco Bonanomi has also been involved with the Tipo 6's test programme.
Vernay said: "We're all very happy, it was a super productive session. We were lucky to have some great weather which meant we could run the car properly.
"We continued to improve the car set-up, but all the systems are working well.
"It was also the first time for Alejandro behind the wheel of the Tipo 6 LMH - Competizione and was a great opportunity for me and our group of great engineers to introduce everything to him.
"We're looking forward to the next test and to the first race in Qatar."
A team statement said that three of the four FIA homologation phases have now been concluded.
Duqueine will remain in the ELMS P2 class next season, where it will face Vector Sport.
The British squad's boss Gary Holland told Autosport that Vector still has ambitions to race in the WEC's Hypercar class in 2025.
