What is "duck test"

n. (context US idiomatic English) for application of common sense and/or intuition regardless of technical parameters.

The Duck test is a humorous term for a form of abductive reasoning. This is its usual expression: The test implies that a person can identify an unknown subject by observing that subject's habitual characteristics. It is sometimes used to counter abstruse, or even valid, arguments that something is not what it appears to be.