Storybook is an open-source tool that provides a sandbox to develop and visualize components in isolation. See the Storybook site for more information about the tool.
The Gutenberg project uses Storybook to view and work with the UI components developed in the WordPress packages.
View online at: https://wordpress.github.io/gutenberg/
Run locally in your development environment running: npm run storybook:dev from the top-level Gutenberg directory.
StoryShots adds automatic Jest Snapshot Testing for Storybook.
Please refer to Testing Overview to learn how to maintain auto-generated unit tests from stories added to Storybook.