The best way to test any set of colors is to swatch them. I have two swatch charts you can download for free. The first one is for a set of 72 colors, however, it will work for sets smaller than that number as well. I used it to swatch and test the set of 36 Prang colored pencils from the Dollar Tree.
The second chart is more detailed and tests for layering, blending, and color mixing.
Download the free PDF Colored Pencil Chart [pencil chart]
Download the free PDF Colored Pencil Testing Chart [testing chart]
The video below shows swatching of the Prang colored pencils and thoughts on how they preform.