Look for previous water damage. Visible mold growth is found behind walls or underneath materials where water has damaged surface. Look for discoloration and leaching from plaster. Testing is not recommended as the first step to determine if you have a mold problem. Reliable sampling for mold can be expensive and requires equipment not available to the general public.
Few standards are available for judging what is an acceptable quantity of mold.
All locations contain some outdoor levels of mold. Unless the source of moisture is removed and the contaminated area is cleaned and disinfected, mold growth is likely to reoccur. Once you know the problem exists, follow the general cleanup procedures below. Clean, disinfect and dry the moldy area. Bag and dispose of any material that has moldy residues, such as rags, paper, leaves or debris.