Frontend testing used to sound simple: open a page, find an element, click it, and verify the result. That description still works for basic workflows, but modern interfaces are no longer a single static DOM that changes in obvious ways. Components can render inside Shadow DOM.
Source: [Dev.to](https://dev.to/mellowthunder735/modern-frontend-testing-is-mostly-about-state-timing-and-geometry-4f7g)