It was in a pretty safe looking box, and the box wasn't beat up, so it must have gone through quality control like that.
One often made mistake is seeing the packer's sign off and thinking that is the QC check list. It is just an assurance that all the items that were supposed to be in the box were in the box.
100% testing of each individual product off an assembly line by the quality control department is not practiced for any consumer item to my knowledge.
Quality control uses statistical analysis. Usually 10 (or some predetermined number) items of a manufacturing lot of 100 to 1,000 will be checked. If all 10 pass then it is assumed they are all the same. If one fails then the whole lot goes back for rework.
Some manufactured items go through a system of multiple tests throughout the manufacturing process. These are usually adjustment stages to bring the product into the range of the 'published specifications.' Some manufacturers may allow for more vibration or other 'defects' than others.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)