Scary question without more information but...
Your Dielectric Withstand Test uses 677 Vdc (or 479 Vac). If the test passes it will confirm that the smallest gap between exposed conductors in the cable is likely greater than 0.003 inches (0.08 mm). If the test fails you may have a gap less than 0.003 inches (0.08 mm). If the DWV test is done in helium then the test might detect a gap as large as 0.083 inches (2.11 mm).