Andy Pettitte will test his cranky left groin Friday with a throwing session that will begin on flat ground and hopefully progress all the way up the pitching mound.

The fact that Joe Girardi will eyeball the workout tells you it’s more than routine.

Pettitte has been idle since July 18 and hasn’t been able to push off the mound as strong as he would like in two mound sessions.

“It’s step one in the process,’’ GM Brian Cashman said. “It’s one hurdle we need to clear.’’

If Pettitte comes through it OK, the Yankees may simulate game conditions soon then send him on a minor-league rehab assignment.

But there is no guarantee the Yankees’ second best starter when he was hurt will be able to push off the mound to his satisfaction.

Pettitte, 11-2 with a 2.88 ERA in 18 starts, was having a Cy Young-type year when injured. When Pettitte left, the Yankees were 58-33. Without him, they are 20-16.