life.rb

require 'set'

class Life
  attr_accessor :state

  def initialize(previous_state)
    @state = advance(previous_state)
  end

  def advance(previous_state)
    next_state = Set.new

    previous_state.each do |cell|
      num_neighbors(cell)
    end
  end

  def num_neighbors(cell)
  end

end

describe "life" do
  context "with an empty state" do
    let(:life) { Life.new(Set.new) }

    it "is not nil" do
      expect(life).to_not be_nil
    end

    it "has a state" do
      expect(life.state).to eql(Set.new)
    end
  end

  context "with a single live cell" do
    let(:grid) { Set.new.add([0,0]) }
    let(:life) { Life.new(grid) }

    it "dies on the next cycle" do
      expect(life.advance(grid)).to eql(Set.new)
    end
  end

  context "with a 4x4 grid and 4 live cells" do
    let(:grid) { Set.new.add([0,0]).add([0,1]).add([1,0]).add([1,1]) }
    let(:next_grid) { Set.new.add([0,0]).add([0,1]).add([1,0]).add([1,1]) }
    let(:life) { Life.new(grid) }

    it "to live forever" do
      expect(life.advance(grid)).to eql(next_grid)
    end
  end
end