1. A test preprocessing method comprising: detecting a brightness of a specimen based on image of the specimen acquired by capturing the image by backlight image capture by an image acquisition unit before test processing of the specimen, and detecting a chylous state of the specimen based on the brightness; controlling the image acquisition unit such that the image acquisition unit repetitively performs the backlight image capture while adjusting a shutter speed until the brightness of the image reaches a predetermined value; detecting the chylous state based on the shutter speed value in a state in which the brightness has reached the predetermined value; detecting a hue of the specimen based on the image captured at the shutter speed in the state in which the brightness has reached the predetermined value; and detecting a hemolytic state of the specimen based on the hue.