You can't test the surface of the green per rule 16. Here's an excerpt (see 16-1d).
a. Touching Line of Putt
The line of putt must not be touched except:
(i) the player may remove loose impediments, provided he does not press anything down;
(ii) the player may place the club in front of the ball when addressing it, provided he does not press anything down;
(iii) in measuring - Rule 18-6;
(iv) in lifting or replacing the ball - Rule 16-1b;
(v) in pressing down a ball-marker;
(vi) in repairing old hole plugs or ball marks on the putting green - Rule 16-1c; and
(vii) in removing movable obstructions - Rule 24-1.
(Indicating line for putting on putting green - see Rule 8-2b.)
b. Lifting and Cleaning Ball
A ball on the putting green may be lifted and, if desired, cleaned. The position of the ball must be marked before it is lifted, and the ball must be replaced (see Rule 20-1).
c. Repair of Hole Plugs, Ball Marks and Other Damage
The player may repair an old hole plug or damage to the putting green caused by the impact of a ball, whether or not the player's ball lies on the putting green. If a ball or ball-marker is accidentally moved in the process of the repair, the ball or ball-marker must be replaced. There is no penalty, provided the movement of the ball or ball-marker is directly attributable to the specific act of repairing an old hole plug or damage to the putting green caused by the impact of a ball. Otherwise, Rule 18 applies.
Any other damage to the putting green must not be repaired if it might assist the player in his subsequent play of the hole.
d. Testing Surface
During the stipulated round, a player must not test the surface of any putting green by rolling a ball or roughening or scraping the surface.
Exception: Between the play of two holes, a player may test the surface of any practice putting green and the putting green of the hole last played, unless the Committee has prohibited such action (see Note 2 to Rule 7-2).
Here's a pretty funny ruling: you can remove an acorn on the green but not repair the depression caused by the falling acorn.
16-1a/7 Player Repairs Depression on Line of Putt Created When Partially Embedded Acorn Removed
Q. A player removed with his hand an embedded acorn on his line of putt. The acorn was not solidly embedded, so it was a loose impediment. The player then repaired the depression in which the acorn lay. Was the repair of the depression a breach of Rule 16-1a?
p.s. here's a link to the rules. http://www.usga.org/Rule-Books/Rules-of-Golf/Rules-and-Decisions/