Building new fields or views is very simple in Odoo. In just a few lines of XML, you can define a new view. However, under the hood, it uses JavaScript in large amounts. Modifying/adding new features on the client side is complex, and it might break a few things. Most of the client-side issues go unnoticed, as most errors are only displayed in the console. So, QUnit test cases are used in Odoo to check the correctness of different JavaScript components.