Implementation of quick sort in Ruby

quick_sort.rb

require 'rspec'

def q_sort(list)
	list = Array(list)
	case list.length
	when 0
		[]
	when 1
		list
	when 2
		if list.first < list.last
			list
		else
			list.reverse
		end
	else
		head = list.first
		tail = list.last(list.length - 1)

		q_sort(tail.select{|x| x <= head}) + Array(head) + q_sort(tail.select{|x| x > head})
	end
end

describe "q_sort" do
	it 'should return empty array for nil' do
		list = nil
		expect(q_sort list).to eq []
	end
	it 'should return empty array for empty array' do
		list = []
		expect(q_sort list).to eq []
	end
	it 'should return same array for 1 length array' do
		list = [3]
		expect(q_sort list).to eq [3]
	end
	it 'should sort 2 length array' do
		list = [1,6]
		expect(q_sort list).to eq [1,6]
	end
	it 'should sort 2 length array' do
		list = [9,6]
		expect(q_sort list).to eq [6, 9]
	end
	it 'should do sort' do
		list = [1, 10, 4, 6, 7, 3, 2]
		expect(q_sort list).to eq [1, 2, 3, 4, 6, 7, 10] 
	end
	it 'should do sort even containing duplicate value' do
		list = [1, 10, 3, 3, 4, 10, 6, 3, 7, 3, 2]
		expect(q_sort list).to eq [1, 2, 3, 3, 3, 3, 4, 6, 7, 10, 10] 
	end

end