How do you test a design system?

I've inherited a component library that I'm bringing back to life.

In the past I've worked on React component libraries and used tools like Storybook to develop them. Testing these is pretty easy - I tend to use mostly react-testing-library and jest.

But this particular library is differenteach component is:

• a scss file for styling
• optionally, some javascript
• a markdown file that combines written guidance for using the component with code samples and live previews

It's not that different from the GOV.UK design system.

Testing the javascript parts is easy enough, but it's only a small part of the overall library.

How do you go about testing something like this in a robust way?