Test your PRNG for collision frequency

prng-collision-test.js

var num = (len, rng) => Math.floor(10 ** (len - 1) + rng() * 9 * 10 ** (len - 1));

var test = (rng, times) => {
  
  var map = {}
  for(let i=0; i<times; i++){
    let rn = rng()
    map[rn] =  map[rn] ? map[rn] + 1 : 1
  }
  let collisions = Object.values(map).filter(val => val > 1)
  let total = collisions.reduce((a,b) => a + b, 0) - collisions.length
  console.log(total)
}