jQuery UI Tests
Unit tests exist for all functionality in jQuery UI. The unit tests can be run locally (some tests require a web server with PHP) to ensure proper functionality before committing changes. The unit tests are also run on TestSwarm for every commit.
Visual tests only exist in cases where we can't verify proper functionality with unit tests. These may be either purely visual or just hard to automate. Most visual tests will provide a description of what is happening on the page and what to look for.