 Examination of the firearm may be as simple as visually inspecting it (defective components may fail in a spectacular manner, resulting in an explosion of the firearm) or may involve more in-depth examination, at the option of the tester.Because proof testing may or may not result in the destruction of the test specimen, it falls on the border between destructive testing and nondestructive testing.A proof mark is a mark specific to the manufacturer, importer, or testing facility that is performing the test.