selectRandom.mjs

export default function selectRandom(list, count) {
  if (count < 1) return []

  const pickIndex = Math.floor(Math.random() * list.length)
  const pick = list[pickIndex]
  const remainder = list.filter((item, index) => index !== pickIndex)

  const result = [pick].concat(selectRandom(remainder, count - 1))

  return result
}

selectRandom.test.mjs

import { strict as assert } from 'node:assert'
import selectRandom from './selectRandom.mjs'

const assertIncludes = (list, target) => {
  assert(list.find(member => member === target))
}

export const selectRandomTest = {
  'returns the only result from a list of one': () => {
    const a = Symbol('a')
    const result = selectRandom([a], 1)

    assert.equal(result.length, 1)
    assert.equal(result[0], a)
  },

  'returns all results from a list of three': () => {
    const a = Symbol('a')
    const b = Symbol('b')
    const c = Symbol('c')
    const result = selectRandom([a, b, c], 3)

    assert.equal(result.length, 3)
    assertIncludes(result, a)
    assertIncludes(result, b)
    assertIncludes(result, c)
  },

  'returns two different results from a list of three': () => {
    const result = selectRandom([Symbol(), Symbol(), Symbol()], 2)

    assert.equal(result.length, 2)
    assert.notEqual(result[0], result[1])
  }
}