Unlock the Michelin Test Track by reaching the Professional level in Single Player -> Gotham Career.
Go to Single Player -> Gotham Career -> My Michelin Test Track.
There are 3 disciplines to choose from:
Time Trials (pick 1 of 5 displayed routes)
Get a score for each Discipline.
As SevenDead1ySinz said, you only need to complete 1 lap for Speed Testing and Time Trials (they never end) but Skid Pan requires you to race until a Finish. It doesn't matter how well you do.