Designing, developing and offering ILI takes a lot of time and effort. Are learners benefiting? Assessment of ILI can help answer this question and aid in identifying teaching/learning areas that may need improvement. TRAILS (Tools for Real Time Assessment of Information Literacy Skills) is freely available for teachers and library media specialists. Jon Mueller's (Professor of Psychology, North Central College, Naperville, IL) Assessments of Information Literacy site provides links to many other ILI instruments, some free and others available for a fee.
See Kitty Lucero's attached comments below on a number of the assessment instruments on Mueller's website.