Duck test

making sure a classifier is based on observables instead of expediency or arbitrariness

The duck test is a type of test that determines whether an unknown thing acts like another thing. More specifically, this test is a form of abductive reasoning, a type of strategy that aims to simplify a conclusion. The duck test is usually written in this expression:

Mallard duck swimming in a lake
A mallard looking like a duck and swimming like a duck.

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

If an unknown subject looks like something that is very similar to a familiar thing, then that unknown subject is concluded to be that familiar thing. In the above example, an unknown subject who swims like a duck and quacks like a duck likely is a duck. The duck test can be used to identify similar cases.

The duck test can be used to identify an unknown subject by observing the common habits of that subject. Sometimes, the duck test can be used to prove that the subject is actually not what what it appears to be.