I work in clothing production. There are literally tests for every kind of durability you can imagine, made to simulate real-world wear and tear. You send in sample garments from bulk production to a company that specializes in these tests and they put them on a machine that replicates say, two pieces of fabric rubbing against each other 1000 times, or pulling on a button until it pops off. Only some of these tests are legally required (the button pulling for kidswear, for example) but they are available to any brand that wants to know how durable their clothes are.