Excerpt from USGA Position on Raking a Similar Hazard – 4/8/2008

After discussion, the JRC agreed on the following position, effective immediately:
Rule 13-4a prohibits a player from testing the condition of the hazard in which his ball lies or a similar hazard. Yet Exception 3 to the Rule, which was introduced in 2008, allows a player to test the condition of one hazard after playing from that hazard into a similar hazard. Although Decision 13-4/0.5 lists smoothing a bunker with a rake, club or otherwise as an example of testing the condition of the hazard, the Etiquette Section of the Rules of Golf provides that "Before leaving a bunker, players should carefully fill up and smooth over all holes and footprints made by them and any nearby made by others."

It is not the intent of Rule 13-4a to prohibit players from practicing the proper etiquette of the game when more than one bunker is involved. Therefore, when the player’s ball lies in a bunker, it would not be a breach of the Rules if the player were to smooth the sand in another bunker, provided (a) the smoothing is for the purpose of tidying up the bunker, (b) the smoothing does not breach Rule 13-2 (Improving Lie, Area of Intended Stance or Swing, or Line of Play) with respect to his next stroke and (c) there is not a reasonable possibility that the smoothing could affect a subsequent stroke by the player.

If the player were to smooth sand in the bunker in which his ball lies prior to making his first stroke in that bunker, he would be in breach of Rule 13-4a.