The short answer
The test plan should reflect where the device is worn and used. Drops, temperature, sweat, button use, charging and long-running software can each create different risks.
In more detail
During development, we use tests to find weaknesses and check the changes made to fix them. The method, sample count and pass criteria should be written down.
Production checks can then focus on the items that matter for consistent builds. Test duration and stress levels need to suit the product, rather than follow one fixed rule for every device.