The 28-year-old New Zealander had a seat fitting with the Ganassi team late last year and comes fresh from a podium finish in Hyderabad's opening round of the 2023 ABB FIA Formula E World Championship in India. He currently sits fifth in the Formula E standings.
Post-Hyderabad, Cassidy travelled to Florida to be part of the two-day test, where he'll drive a Honda-powered Dallara IR18 around the 1.7-mile (2.73km) short course.
“We're excited to be able to test Nick and owe a debt of gratitude to IndyCar and Nick's team for making this happen,” said CGR managing director, Mike Hull.
“This is all in an effort to understand the driver landscape going into 2024 so we can be ready.
Cassidy could be a candidate for a 2024 Ganassi IndyCar seat given that his current contract with Envision Racing – who he's been racing in Formula with since 2020 – expires at the end of this season.
That opportunity may well arise given the highly publicised controversy surrounding Ganassi driver Alex Palou and his attempted defection to McLaren last season. Palou's due to see out his Ganassi drive this season and is a free agent for 2024.
In addition to last weekend's podium, Cassidy won a chaotic New York City E-Prix last year, which was interrupted by a downpour on the Brooklyn Streety Circuit and finished on the podium in London only weeks later.
He also has titles in Japanese Formula 3, Super GT and Super Formula to his name.
CGR also tested Ferrari Junior Robert Shwartzman at Sebring in January, the Israeli-Russian driver clocking the fastest lap (52.539s) in what was a four-car hit-out, with 2022 Indy Lights (now Indy NXT) runner-up Sting Ray Robb next-quickest (52.584s) in the sole Dale Coyne Racing entry.
The Sebring booking private test follows an open test at the Thermal Club in Palm Springs, where the 27-car field ran in what was the first pre-season IndyCar test since 2020.
The first IndyCar race of 2023 takes place in St Petersburg on March 6.