1_spec.rb

Painting = Struct.new(:name, :year)

def first(list, sorter = nil)
  list = list.sort(&sorter) if sorter
  list.first
end

def rest(list, sorter = nil)
  list = list.sort(&sorter) if sorter
  _, *rest = list
  rest
end


describe Painting do
  let(:one) { Painting.new("Spanish Couple In Front Of Inn", 1900) }
  let(:two) { Painting.new("Guernica", 1937) }
  let(:three) { Painting.new("Petite Fleurs", 1958) }
  let(:paintings) { [one, two, three] }
  let(:by_name_sorter) { ->(p1, p2) { p1.name <=> p2.name } }

  it "should return the first element" do
    expect(first(paintings)).to eq(one)
  end

  it "returns the rest of the elements" do
    expect(rest(paintings)).to eq([two, three])
  end

  it "should return the first element with sorter" do
    expect(first(paintings, by_name_sorter).name).to eq("Guernica")
  end

  it "returns the rest of the elements with sorter" do
    expect(rest(paintings, by_name_sorter).map(&:name)).to eq([
          "Petite Fleurs",
          "Spanish Couple In Front Of Inn"
        ])
  end

  context 'sorter tests' do
    it 'sorts by name' do
      expect(by_name_sorter.call(one, two)).to eq(1)
      expect(by_name_sorter.call(two, three)).to eq(-1)
    end
  end
end