Testing products properly is HARD. Companies have entire groups of people who that is their entire job and if they do it wrong it can costs millions in returned product. At the same time, if the test is too harsh, the customer is paying extra for a product that is over-designed for conditions the product will never experience.
For example, with his bending test. You would define a standard loading method (e.g. 3 point or 4 point with specific spacing), and then apply a realistic load a phone may experience plus some safety factor with a specific loading/unloading profile (say a phone is sat on and experiences 100lbf you might test to 125lbf). Once released you inspect the phone for damage, deformation, and test functionality.