Here are a few UML (Unified Modeling Language) diagrams that show a bit about how Visual FlexUnit works. All are simplified to enhance clarity. This post is intended to complement my Highlights of Visual FlexUnit’s Code post. 1. TestCase Classes When you use VFU to write visual tests you subclass VfuTestCase rather than TestCase. But VfuTestCase is a subclass of TestCase, so you still have access