code: function rep (num, str) {
    return function (arr, done) {
      arr.forEach(function (i, idx) {
        var s = ''
        if (typeof i === 'string') s = i
        if (idx === 0) return
        else if (idx/num === Math.floor(idx/num)) arr[idx] = s + str
      })
      done()
    }
  }
docs: Work for tests