Holiday Testing, also known as Wet Sponge Testing or Spark Testing, is an inspection method used to detect defects (such as pinholes or tiny pores) on surfaces coated with corrosion-resistant materials, like paint, rubber lining, or internal coatings of tanks or pipes. The process involves applying low or high voltage electricity across the coated surface. If there is a defect, leak, or an area where the coating is too thin, the device immediately triggers an audible or visual alarm.