testing.rb

def assert(actual, expected)
  raise "Expected #{actual.inspect} to equal #{expected.inspect}" unless actual == expected
end

LIVE = 'X'
DEAD = 'O'
def evolve(board)
  board.map.with_index do |row, x|
    row.map.with_index do |p, y|
      if p == LIVE
        puts get_live_count(x, y, board)
        ([2,3].include?(get_live_count(x, y, board))) ? LIVE : DEAD
      else
        DEAD
      end
    end
  end
end

def get_live_count(x, y, board)
  neighbors = get_neighbors(x, y)
  filter_neighbors(neighbors, board).count { |rindex, cindex| board[rindex][cindex] == LIVE }
end

def filter_neighbors(neighbors, board)
  neighbors.select do |rindex, cindex|
    rindex >= 0 && rindex < board.length && cindex >= 0 && cindex < board[rindex].length
  end
end

def get_neighbors(x, y)
  [
  [x, (y+1)],
  [x, (y-1)],
  [(x-1), y],
  [(x+1), y],
  [(x+1), (y+1)],
  [(x-1), (y-1)],
  [(x+1), (y-1)],
  [(x-1), (y+1)]
]
end

# Rule #1
assert(evolve([%w(X O), %w(O O)]), [%w(O O), %w(O O)])
assert(evolve([%w(O O), %w(O X)]), [%w(O O), %w(O O)])
assert(evolve([%w(O O O), %w(O X O), %w(O O O)]), [%w(O O O), %w(O O O), %w(O O O)])

# Rule 2
assert(evolve([%w(X X X)]), [%w(O X O)])
assert(evolve([%w(O X O), %w(O X O), %w(O X O)]), [%w(O O O), %w(O X O), %w(O O O)])
assert(evolve([%w(O X O), %w(O X X)]), [%w(O X O), %w(O X X)])
assert(evolve([%w(O X O), %w(X X O)]), [%w(O X O), %w(X X O)])
#Here ends pairing

assert(evolve([%w(X O X), %w(O X O), %w(X O O)]), [%w(O O O), %w(O X O), %w(O O O)])

#Rule 3
assert(evolve([%w(X O X), %w(O X O), %w(X O X)]), [%w(O O O), %w(O O O), %w(O O O)])
puts "Test passed."