Move an array item to specified index

array_ordering.rb

module ArrayOrdering
  # Returns clone of the array with subject moved into the new idx
  def self.move_to_position(_list, subject, new_idx)
    old_idx = _list.index(subject)

    return _list unless old_idx != new_idx

    list = _list.clone

    if old_idx.nil?
      list.insert(new_idx, subject)
    else
      list.insert(new_idx, list.delete_at(old_idx))
    end
  end
end

array_ordering_spec.rb

require 'minitest/autorun'
require_relative './array_ordering'

class ArrayOrderingTest < Minitest::Test
  describe ArrayOrdering do
    let(:first) {1 }
    let(:second) { 2 }
    let(:third) { 3 }
    let(:fourth) { 4 }
    let(:list) { [first, second, third, fourth] }

    it 'swaps with first position' do
      sorted = ArrayOrdering.move_to_position(list, second, 0)
      assert sorted.eql? [second, first, third, fourth]
    end

    it 'moves to first position' do
      sorted = ArrayOrdering.move_to_position(list, third, 0)
      assert sorted.eql? [third, first, second, fourth]
    end

    it 'swaps lower' do
      sorted = ArrayOrdering.move_to_position(list, third, 1)
      assert sorted.eql? [first, third, second, fourth]
    end

    it 'moves lower' do
      sorted = ArrayOrdering.move_to_position(list, fourth, 1)
      assert sorted.eql? [first, fourth, second, third]
    end

    it 'leaves in place' do
      sorted = ArrayOrdering.move_to_position(list, third, 2)
      assert sorted.eql? [first, second, third, fourth]
    end

    it 'swaps higher' do
      sorted = ArrayOrdering.move_to_position(list, second, 2)
      assert sorted.eql? [first, third, second, fourth]
    end

    it 'moves higher' do
      sorted = ArrayOrdering.move_to_position(list, first, 2)
      assert sorted.eql? [second, third, first, fourth]
    end

    it 'swaps with last position' do
      sorted = ArrayOrdering.move_to_position(list, third, 3)
      assert sorted.eql? [first, second, fourth, third]
    end

    it 'moves to last position' do
      sorted = ArrayOrdering.move_to_position(list, second, 3)
      assert sorted.eql? [first, third, fourth, second]
    end

    # it 'moves to last position when move index is greater then list length' do
    #   sorted = ArrayOrdering.move_to_position(list, second, 999)
    #   assert sorted.eql? [first, third, fourth, second]
    # end

    it 'inserts new items into the array' do
      fifth = 5
      sorted = ArrayOrdering.move_to_position(list, fifth, 1)
      assert sorted.eql? [first, fifth, second, third, fourth]
    end
  end
end