PAT Testing in a nutshell
Portable appliance testing, PAT testing or PA Testing is a process used to check electrical equipment is safe to use, through doing a series of inspections by a competent person and tests using a machine
Electrical appliances are (generally) manufactured to be safe, and should continue to be so throughout their life but issues do occur – generally speaking they can get damaged, dropped, broken, kicked, wet, cold, etc leading to issues occurring. The purpose of the PAT Test is to check if what has occurred will cause any problems. Such as has the internal insulation or earthing been effected, or externally has the appliance incurred damage that could prove dangerous.
A skilled person with suitable knowledge will be able to find such issues by looking at the appliance and through the readings achieved by their testing machine.
PAT is not a legal requirement (nor are many things we do) but it is important because it finds these faults and fixes them, thus removing the danger. By removing danger, and thus making safe the fault the appliance maintains the level of safety needed, keeping the equipment provider compliant with legislations.