Are you ready to test your skills as a human fuzzer? Here’s a collection of puzzles where the objective is to find an input that leads to the execution of what appears to be dead code.

• JavaScript
  • Puzzle 1: Cyclic ordering
  • Puzzle 2: And but not Or
  • Puzzle 3: Sort descending by default
• Python
  • Puzzle 4: To be and not to be

JavaScript

Puzzle 1: Cyclic ordering

function f(a, b, c) {
	if (a < b && b < c && c < a) {
		throw Error();
	}
}

Goal: Find values for a, b and c such that f(a,b,c) throws an error.

Constraint: All input values should be of primitive type (i.e. not objects or arrays).

Puzzle 2: And but not Or

function f(a, b) {
	if (a > b || a == b) {
		return true;
	} else if (a >= b) {
		throw Error();
	} else {
		return false;
	}
}

Goal: Find values for a and b such that f(a, b) throws an error.

Constraint: All input values should be of primitive type (i.e. not objects or arrays).

Puzzle 3: Sort descending by default

function f(a, b) {
	var min = a <= b ? a : b;
	var max = a >= b ? a : b;
	var [first, second] = [a, b].sort();

	if (a != b && first === max && second === min) {
		throw Error();
	}
}

Goal: Find values for a and b such that f(a, b) throws an error.

Constraint: All input values should be of primitive type (i.e. not objects or arrays).

Python

Puzzle 4: To be and not to be

def h(x, y):
  return x is y+1

def g(x):
  return h(x, x-1)

def f(x):
  if g(x) and not g(x+1):
    raise Exception()

Goal: Find a value for x such that f(x) raises an exception.

Constraint: The input value is of a primitive type (i.e. it is a number). Use the reference implementation of Python (aka CPython).

Hint: No solutions exist on some other implementations of Python such as PyPy.

Credit to Kevin Laeufer for introducing me to this phenemenon.