Component testing is 3 dimensional, requiring interactions, visual, and accessibility. Interactions include the program functionality and operating in the manner you sought for it. Visual includes the vision of the program and there aren't assets you like for the UI. Finally, accessibility is the ability to make the program follow regulations and enable users to access it. The importance of testing is to ensure you're demonstrating a product that consumers can utilize.
Storybook enables the user to design programs feasibly and modify the program at different scales. This can be at the smallest level or alternatively on a larger scale.