Sinon.JS provides extensible test spies that can record many different aspects of a function execution, including calling parameters, return values, and thrown exceptions. The basic developer workflow is to create a spy, hook it into a function under test, execute the function, and then verify that the spy's recorded information matches with the test expectations. In this section, we will walk through the different ways to create spies and discuss some of the most useful parts of the Sinon.JS spy API.