YouTuber JerryRigEverything regularly performs scratch tests to many smartphones to try the durability of materials used on various components like the LED flash lens, camera lens, buttons, keys, and earpiece. He also performs burn tests to the display to somewhat simulate degradation of the pixels over time. And finally, a bend test is performed to test the phones internal structure.
Apples infamous bendgate was a topic of controversy back when users began reporting that their iPhone 6 Plus became bent all of a sudden, just by either sitting on it or applying just intentional pressure. This has since sparked the birth of the bend test and smartphone makers began taking this issue into account when designing a smartphones internal structure.
Upon testing the camera lens and home key with Mohs hardness picks, it is concluded that neither the home button nor the camera lens (both of which were made of sapphire glass in the iPhone 6S) are made of sapphire glass. Both the home key and camera lenses began scratching with around a Mohs hardness of 6, just like the display glass.
Apples spec page lists the iPhone 7 to have a sapphire crystal lens, but we now know that this is not the case. Perhaps Apple plans to use real sapphire on the lens once the demand for iPhones slows down. The process probably takes longer than crafting the component from display glass.