In addition to "real world" testing, we took these bags to a parking lot and tested the wheels on both cracked asphalt and gravel surfaces. We examined each bag's wheels, researched the materials they were made out of, and assessed their zippers. We raised and lowered their handles at least 25 times to compare their sturdiness, or lack thereof, and loaded them up with books and let them plop down stairs just to make sure the wheels wouldn't crack under pressure.
We compared the different models' features head-to-head in several pack tests. Our first pack test was for a "wintertime long weekend." Could the bags hold everything we would need for three days in winter (when clothing is bulkier), including two pairs of pants, four tops/sweaters, a pair of running shoes, workout clothes, and a nice outfit (either a fancy dress with heels or business attire)? We also included socks and undergarments, a toiletry bag, a large novel, and a laptop. Some bags held all these items with room to spare and others required some serious shoving (and still didn't hold everything).
We also performed a "pack for a week in our carry-on luggage" test, which included: four pairs of pants, ten shirts, four pairs of shoes, two jackets/sweater, and two toiletry bags. We tested the four-wheeled bags by trying to make figure 8s on a hardwood floor and compared the turning radii of the two-wheeled models. Finally, we researched all the materials used, counted the pockets, measured the handles, and considered each bag's style.