Difficult. IANAFD so this may be slightly technically inaccurate:

We got them to actually draw something (called a flat) from a half-drawn garment, draw a full flat from scratch, identify trends from a series of photos, pick textile colours from photos, identify designers from "signature" garments, have them debug a spec. to see if a garment was reasonable (say the spec called for a notion like a chunky zip on an unsuitable fabric), and a few other things.