1. A method which tests an operation state of an electron beam inspection apparatus, comprising: scanning at least one scan line on a predetermined inspection area of a substrate with an electron beam and detecting secondary electrons emitted from the at least one scan line; generating at least one inspection image corresponding to the at least one scan line from the detected secondary electrons; analyzing the at least one inspection image using an initial sensitivity and generating an inspection graph indicating the detected number of defects on the at least one scan line; and comparing the inspection graph with a reference graph to determine if the initial sensitivity needs to be adjusted.