On 8 December 2005, Karthikeyan tested for Williams at Spain and finished a respectable fifth, outpacing the confirmed Williams second driver, Nico Rosberg in the FW27C chassis, who finished ninth.
O 8 de decembro de 2005, Karthikeyan probou co Williams en España e terminou nun respectable quinto posto, superando ao segundo piloto de Williams, Nico Rosberg no FW27C, que terminou noveno.