What is icon testing?
Users presented with an icon must guess what that icon symbolizes. In some ways, this is the icon version of a Rorschach inkblot test. The purpose of this test is to make sure that icons are recognizable, and that people can easily deduce the object that it depicts.
How would you measure the usability of icons?
Time to Locate: Ask participants to find a function or complete an action using the icons as presented in the context of an application. This is more like a classic findability study or click test. Time how long it takes users to successfully click on the correct icon as a measure of success.