Is there tests for cellulitis?

No. Just clinical exam of swelling het and redness not associated with a vein problem. See a doctor if there is any chance that you have cellulitis.
What's the cause? Cellulitis is basically a visible inflammation (itis) of the skin and soft tissues (red, hot, swollen and tender) . It can be caused by many things including sunburn (radiation), trauma (sprained ankle) or poor vein circulation (stasis dermatitis). It need not be caused by bacteria. If you have repeated episodes of this, get to a wound care or vascular specialist, the diagnoses you have is wrong.
Tests for cellulitis. Cellulitis is a condition of the skin; the tests that are run are cultures and sensitivity and blood tests for both aerobic and anerobic bacteria.