old_contents: import engine
  
  
  VALID_COORDS = [(x, y) for x in xrange(97, 105) for y in xrange(49, 57)]
  INVALID_COORDS = [
      (0, 0), (-1, -1),
      (96, 49), (96, 48),
      (105, 49), (104, 48),
      (96, 56), (97, 57),
      (105, 56), (104, 57)
      ]
  VALID_A1 = [chr(x) + chr(y) for x in xrange(97, 105) for y in xrange(49, 57)]
  INVALID_A1 = ['a0', 'a9', 'h0', 'h9', 'z1', 'z8']
  
  
  def test_coord_to_a1():
      u"""Assert the coord-to-a1 dictionary has only the desired keypairs."""
      for coord in VALID_COORDS:
          assert engine._coord_to_a1.get(coord, False) is not False
      for coord in INVALID_COORDS:
          assert engine._coord_to_a1.get(coord, False) is False
  
  
  def test_a1_to_coord():
      u"""Assert the a1-to-coord dictionary has only the desired keypairs."""
      for a1 in VALID_A1:
          assert engine._a1_to_coord.get(a1, False) is not False
      for a1 in INVALID_A1:
          assert engine._a1_to_coord.get(a1, False) is False
  
  
  def test_is_coord_on_board():
      u"""Assert that only valid coords are considered in the board."""
      for coord in VALID_COORDS:
          assert engine._is_coord_on_board(coord) is True
      for coord in INVALID_COORDS:
          assert engine._is_coord_on_board(coord) is False
  
  
  def test_instantiate_Piece():
      u"""Assert an instance of Piece has the expected attributes."""
      for coord in VALID_COORDS:
          p = engine.Piece(coord)
          assert isinstance(p, engine.Piece)
          assert p.x, p.y == coord
  
  
  def test_instantiate_SimpleUnit():
      u"""Assert an instance of SimpleUnit has the expected attributes."""
      for color in ['white', 'black']:
          for coord in VALID_COORDS:
              p = engine.SimpleUnit(coord, color)
              assert isinstance(p, engine.SimpleUnit)
              assert p.x, p.y == coord
              assert p.color == color
  
new_contents: import engine
  
  
  VALID_COORDS = [(x, y) for x in xrange(97, 105) for y in xrange(49, 57)]
  INVALID_COORDS = [
      (0, 0), (-1, -1),
      (96, 49), (96, 48),
      (105, 49), (104, 48),
      (96, 56), (97, 57),
      (105, 56), (104, 57)
      ]
  VALID_A1 = [chr(x) + chr(y) for x in xrange(97, 105) for y in xrange(49, 57)]
  INVALID_A1 = ['a0', 'a9', 'h0', 'h9', 'z1', 'z8']
  EMPTY_BOARD = dict([((x, y), None) for x in xrange(97, 105) for y in xrange(49, 57)])
  
  
  def test_coord_to_a1():
      u"""Assert the coord-to-a1 dictionary has only the desired keypairs."""
      for coord in VALID_COORDS:
          assert engine._coord_to_a1.get(coord, False) is not False
      for coord in INVALID_COORDS:
          assert engine._coord_to_a1.get(coord, False) is False
  
  
  def test_a1_to_coord():
      u"""Assert the a1-to-coord dictionary has only the desired keypairs."""
      for a1 in VALID_A1:
          assert engine._a1_to_coord.get(a1, False) is not False
      for a1 in INVALID_A1:
          assert engine._a1_to_coord.get(a1, False) is False
  
  
  def test_is_coord_on_board():
      u"""Assert that only valid coords are considered in the board."""
      for coord in VALID_COORDS:
          assert engine._is_coord_on_board(coord) is True
      for coord in INVALID_COORDS:
          assert engine._is_coord_on_board(coord) is False
  
  
  def test_instantiate_Piece():
      u"""Assert an instance of Piece has the expected attributes."""
      for coord in VALID_COORDS:
          p = engine.Piece(coord)
          assert isinstance(p, engine.Piece)
          assert p.x, p.y == coord
  
  
  def test_instantiate_SimpleUnit():
      u"""Assert an instance of SimpleUnit has the expected attributes."""
      for color in ['white', 'black']:
          for coord in VALID_COORDS:
              p = engine.SimpleUnit(coord, color)
              assert isinstance(p, engine.SimpleUnit)
              assert p.x, p.y == coord
              assert p.color == color
  
  
  def test_SimpleUnit_possible_moves_empty_space():
      u"""Assert only valid moves are returned."""
      p = engine.SimpleUnit(VALID_COORDS[0], 'white')
      board = EMPTY_BOARD.copy()
      board[(p.x, p.y)] = p
      assert p.possible_moves(board) == [(p.x, p.y + 1)]
  
subject: Add test_SimpleUnit_possible_moves_empty_space() to assert that only valid moves are returned