pencil test

Short definition from Wiktionary

Noun

1. 1
   An early version of an animated scene, consisting of rough sketches that are photographed or scanned.
2. 2
   An informal test of whether a girl needs to wear a bra, based on whether a pencil placed in the inframammary fold stays in place or not.
3. 3
   A method of determining racial identity during apartheid, based on how easily a pencil pushed through a person's hair can be removed.