Syria is a civil war, with no direct international implications.

Iran is attempting to find an effective defense against Israeli aggression. Israel is known to attack various nations around the area, including Syria, without provocation. If any other nation acted like Israel we would brand it as "rogue".

Israel has nuclear weapons, is a rogue nation, and Iran would seem to have every right to do what it had to defend itself. No nation with nukes has ever been attacked.

I don't see Syria as a "test" of the US at all. Even a little bit. And I don't think that anyone would gauge the response or lack thereof as an indication of the US response to anything else.

Simply my arrogant opinion, though, based upon what is reported in the media and I believe that can be suspect.