What is a usability test?
A Usability testing consists of observing a representative end user interacting with the products in order to understand how an end user would respond to a software under realistic conditions. This test includes giving the user a goal to reach but no specific instructions as to how the product should be used.
the team records and analyzes the user’s actions without intervening and will take later in consideration any difficulties encountered by the user, illustrating differences between the team’s assumptions and actual behavior.
this practice is far from being only used in agile but it was in 2008 that it was first introduced in it as a trend to incorporate into Agile practice ideas from the user experience design community.