Salesforce has three major releases a year.

 DOM changes introduced by a release can cause automated browser tests to need updating, as they can affect the way the browser interacts with the web page elements and the selectors used to identify them. New standard fields, metadata schema changes, and new Apex methods are not likely to affect automated browser tests, as they are mostly related to the backend functionality and data model of Salesforce. See [Automated Browser Testing] for more details.