Use a Fiber Inspection Microscope – 200–400× magnification reveals scratches or pits on ferrule end-face. Visual Fault Locator (VFL) – Injects a red laser (650 nm); light leakage indicates bend, crack, or break. The process of testing any fiber optic cable plant during and after installation includes all the procedures covered so far. As network speeds and bandwidth demands increase, fiber performance requirements have become more stringent. Corning recommends that all fiber optic systems be tested to a minimum set. Here are the most common fiber optic testing methods used by network professionals: Conducting a visual inspection test involves using a fiber scope or microscope to examine the endfaces of connectors for dirt, scratches, or cracks. Cable contamination can also.