Toro Rosso concede they head to Bahrain with very little idea about what to expect.
The midfield team struggled in the opening pre-season test as, like many of the Renault runners, they were blighted by engine issues and overheating.
The team managed just 54 laps while Jean-Eric Vergne's 1:29.915 put him outside the top ten in 12th place. Daniil Kvyat was 19th quickest for the week.
Toro Rosso's woes reportedly continued during a recent day of filming at Misano circuit in Italy where, according to unconfirmed reports, they suffered repeated stoppages.
As such, the team is not making any predictions ahead of the next outing in Bahrain.
"How do we expect to get on at the tests? Clearly, after the first four days in Jerez, that is a complete mystery," the team said.
"Suffice to say that everyone in Faenza, Bicester and Viry, the latter being home to our Power Unit supplier, has been working flat out."
The team also revealed their line-up for the first Bahrain test with Kvyat up first while Vergne will drive on the final two days.
"For the first of the two tests in the desert, Daniil Kvyat will drive on the first and third days, with Jean-Eric Vergne at the wheel for days two and four."