Hey! You’re right, this part was vague. Testing your design system means testing the coherence of the elements and how they work together: typeface and weight choices, colors, etc. A lot of designers will throw together elements that look good without testing enough variants to ensure they have made choices with optimal synchronicity.

For instance, on a bright color palette heavier font weights are going to be more legible and accessible than lighter ones, but also testing varieties of fonts with and against the colors / imagery, etc is important.

Hope this helps