There are a few reasons you might want to hire a Sinon.JS developer: - To improve the test coverage of your JavaScript codebase - Sinon.JS can be used to create unit tests for your code that verify its functionality independently from the rest of your application. This can help increase confidence in the stability of your code and catch bugs early on. - To stub out external dependencies - If your code relies on calls to an API or other external service, you can use Sinon.JS to stub out those dependencies during testing. This allows you to test your code in isolation and avoid having to set up a complex testing environment. - To mock browser behavior - Sinon.JS can also be used to mock browser behavior, such as XMLHttpRequest objects or the window object. This is useful for testing code that interacts with the DOM or makes Ajax requests, without having to actually load a page in a browser.