Final exercise at Corey Haines' Improving Your TDD workshop

gol.rb

class Board
  def initialize
    @living = []
  end

  def evolve_dead_cells

  end

  def add_living_cell(location)
    @living << location
  end

  def evolve_living_cells
    @living = @living.select {|location| location.neighbor_count == 2}
  end

  def alive_at?(location)
    location.neighbor_count == 3 || @living.include?(location)
  end
end

class Location
  def update_living_cells(living_cells)

  end

  def neighbor_count
    return 0
  end
end

describe "Location" do
  describe "neighbor_count" do
    it "should be zero when there no living cells to choose from" do
      location = Location.new
      location.update_living_cells []
      location.neighbor_count.should == 0
    end
  end
end

describe "Board" do
  describe "evolve_dead_cells" do
    it "does not create in a location that doesnt have neighbors" do
      location_with_0_neighbors = stub :neighbor_count => 0
      board = Board.new
      board.evolve_dead_cells
      board.alive_at?(location_with_0_neighbors).should be_false
    end

    it "creates in a location that has 3 living neighbors" do
      location_with_3_neighbors = stub :neighbor_count => 3
      board = Board.new
      board.evolve_dead_cells
      board.alive_at?(location_with_3_neighbors).should be_true
    end
  end

  describe "evolve_living_cells" do
    it "kills a cell with 0 neighbors" do
      location_with_0_neighbors = stub :neighbor_count => 0
      board = Board.new
      board.add_living_cell location_with_0_neighbors
      board.evolve_living_cells
      board.alive_at?(location_with_0_neighbors).should be_false
    end

    it "keeps a cell with 2 neighbors alive" do
      location_with_2_neighbors = stub :neighbor_count => 2
      board = Board.new
      board.add_living_cell location_with_2_neighbors
      board.evolve_living_cells
      board.alive_at?(location_with_2_neighbors).should be_true
    end

    it "kills a cell with 1 neighbor and keeps one with 2 alive" do
      location_with_2_neighbors = stub :neighbor_count => 2
      location_with_1_neighbor = stub :neighbor_count => 1
      board = Board.new
      board.add_living_cell location_with_2_neighbors
      board.add_living_cell location_with_1_neighbor
      board.evolve_living_cells
      board.alive_at?(location_with_2_neighbors).should be_true
      board.alive_at?(location_with_1_neighbor).should be_false
    end
  end
end