Language or testing frameworks or the lack thereof are no reason not to write tests. All that is needed is a function that calls the function to be checked.

prime-factors.sh

#!/usr/bin/env bash

function assert_array_same {
  if [ "${expected[*]}" != "${actual[*]}" ]; then
    echo -e "\nFailed $1\nExpected: ${expected[*]}\nActual: ${actual[*]}" && exit 1
  else
    echo -en "."
  fi
}


function generate {
  local primes=( )
  local n=$1
  local candidate=2
  while [ $n -gt 1 ]; do
    while [ $((n % candidate)) -eq 0 ]; do
      primes+=($candidate)
      n=$((n / candidate))
    done
    candidate=$((candidate+1))
  done
  echo "${primes[*]}"
}

expected=( )
actual="$(generate 1)"
assert_array_same "one"

expected=( 2 )
actual="$(generate 2)"
assert_array_same "two"

expected=( 3 )
actual="$(generate 3)"
assert_array_same "three"

expected=( 2 2 )
actual="$(generate 4)"
assert_array_same "four"

expected=( 5 )
actual="$(generate 5)"
assert_array_same "five"

expected=( 2 3 )
actual="$(generate 6)"
assert_array_same "six"

expected=( 7 )
actual="$(generate 7)"
assert_array_same "seven"

expected=( 2 2 2 )
actual="$(generate 8)"
assert_array_same "eight"

expected=( 3 3 )
actual="$(generate 9)"
assert_array_same "nine"

expected=( 2 3 3 5 7 7 11 13 )
actual=$(generate $((2 * 3 * 3 * 5 * 7 * 7 * 11 * 13)))
assert_array_same "nine"

echo -e "\nall passed"