 In firearm terminology, a proof test is a test wherein a deliberately over-pressured round is fired from a firearm in order to verify that the firearm is not defective and will not explode on firing.The firearm is inspected after the test, and if it is found to be in sound condition, then it is marked with a "proof mark" to indicate that it has been "proofed" (not "proven").In many jurisdictions a proof test and valid proof mark are required for the sale of firearms.