Test thoroughly to see what someone can do, as in We put the new programmer though her paces, and she passed with flying colors. The idiom can refer to things as well, as in When we put the electrical system through its paces, we blew a fuse. The expression alludes to testing a horse's ability in the various paces (trot, canter, and gallop). Its use referring to horses dates from the late 1700s; its figurative use was first recorded in 1871.