What is this test?
Watch a movie. Read a book. Do what you must to reach the conclusion of a story. At the end of the tale, does a male character (hero) fight a male character (villain) for possession of a female character? (The female character may possess heroic or villainous traits.)
Clarification. No knife need feature in the fight. Some kind of weapon is waved around. One character waves his around. Another character waves his around. The more skilful dick-waving character claims the female.
Further clarification. The female character need not explicitly be referred to as the girl.
"Grab the girl."
"Girl? I'm 25!" (Says 35-year-old actress pretending she's 30, portraying 25-year-old with the mental age of an actual girl if we go by the lines she's handed in the script.)
So. Does the story pass the knife test? If no story-ending dick-waving contest occurs, the test is passed.
Variations? They are legion. The male hero may fight the male villain to convert the female villain to the path of righteousness, and so on.
All three characters could easily be female. Or male. Robots. Asexual sentient slime creatures. Particles of dust. Three characters meet, and there's a fight. Two characters limp away. The story ends.
Yes, I grew tired watching movies featuring two guys having a knife-fight in the rain over a woman referred to as the girl. A younger guy and an older guy. The older more-experienced guy usually croaks it when he runs out of puff.
I know I haven't actually seen that movie. It just feels that way.
Advice? Subvert the knife test at every turn.
Other entries. See also WRITING FICTION. THE WOMAN TEST. For more in that line, try WRITING FICTION. THE CHAPTER TEST. And for a piece on conduct, rather than typing, there's WRITING FICTION. THE CREEPY SEXIST DICK AUTHOR TEST.