A quick pairing exercise with @mattr- to learn a bit more about how to approach tests.

game_of_life_spec.rb

require 'rspec'

class Game
  attr_reader :alive_cells
  def initialize(living_cells)
    @living_cells = {}
    living_cells.each do |coords|
      @living_cells[coords] = Cell.new(true)
    end
  end

  def next_generation
  end

  def number_of_neighbors_for(x, y)
  end

  def alive_cells
    @living_cells.keys
  end
end

class Cell
  attr_accessor :number_of_neighbors
  def initialize(living)
    @alive = living
  end

  def evolve
    @alive = false if number_of_neighbors < 2 || number_of_neighbors > 3
    @alive = true if number_of_neighbors == 3
  end

  def alive?
    @alive
  end
end

describe Game do
  let(:block_cells) { [[0, 0], [0, 1], [1, 0], [1, 1]] }
  let(:blinker_cells_a) { [[0, -1], [0, 0], [0, 1]] }
  let(:blinker_cells_b) { [[-1, 0], [0, 0], [1, 0]] }

  it "stays the same for the block game" do
    game = Game.new(block_cells)
    game.next_generation
    game.alive_cells.should == block_cells
  end

  it "knows how many living neighbors a given cell has" do
    game = Game.new(blinker_cells_a)
    game.number_of_neighbors_for(0, 0).should == 2
  end

  #it "occilates for the blinker game" do
    #game = Game.new(blinker_cells_a)
    #game.next_generation
    #game.alive_cells.should == blinker_cells_b
  #end

  describe "live cells" do
    let(:cell) { Cell.new(true) }
    it "dies if fewer than 2 neighbors" do
      cell.number_of_neighbors = 1
      cell.evolve
      cell.should_not be_alive
    end

    it "lives with two neighbors" do
      cell.number_of_neighbors = 2
      cell.evolve
      cell.should be_alive
    end

    it "lives with three neighbors" do
      cell.number_of_neighbors = 3
      cell.evolve
      cell.should be_alive
    end

    it "dies with more than three neighbors" do
      cell.number_of_neighbors = 4
      cell.evolve
      cell.should_not be_alive
    end
  end

  describe "dead cells" do
    let(:cell) { Cell.new(false) }
    it "becomes alive if exactly three neighbors" do
      cell.number_of_neighbors = 3
      cell.evolve
      cell.should be_alive
    end

    it "stays dead without exactly three neighbors" do
      cell.number_of_neighbors = 2
      cell.evolve
      cell.should_not be_alive
    end
  end
end