The short answer
Agree the acceptance plan before the build. It should cover incoming parts, assembly checks and finished-device tests, with clear limits and a record of the result.
In more detail
For a wearable, the plan may include display and touch, buttons, charging, battery condition, camera, audio and wireless functions. The list follows the actual product specification.
Some items need a test on each unit; others can use an agreed sampling plan. Defect categories, retest rules and batch acceptance should be decided before shipment.