Test recursive factorial function in JavaScript.

factorial.js

const assert = require('assert');

function factorial(n) {
  if (n > 1) {
    return n * factorial(n - 1);
  }
  return 1;
}

assert.equal(factorial(1), 1);
assert.equal(factorial(2), 2);
assert.equal(factorial(3), 6);
assert.equal(factorial(4), 24);
assert.equal(factorial(5), 120);