I suppose they want to verify your ability to planing and make a strategy for testing, See If you have a container full of products how could you verify if they are ok? If they have the standard that the supermarket wants?! You have to make a smart strategy to verify that by sampling. In software, we can use the limit value strategy, the partitions classes method too. With supermarket products, you have to think beyond and make sampling, verify the date of the products, if the products are what was asked ... that kind of thing.