Discrimination tests are used when differences among products are questionable. For example, is there are perceived difference (appearance, aroma, taste, texture or sound) between the two products?
A difference test can be performed with a trained panel, that is familiar with the product category, to detect possible small variances among product samples. This would be useful, when a product is expected to be perceived as the same, when it has undergone small processing, or ingredient changes, or in quality control.
A difference test can also be run with a consumer panel, to establish how large a portion of the users of the product would detect differences between two similar products, if any.