def testNodesMatchingLetter(self):
tiles = [['', '', '', 'x', 'z', 's', '', 'f', '']]
board = Board(tiles)
first_row = board.nodes[0]
placements = Placement.placements('safe', first_row[5])
placement = placements[0]
nodes = Collision.nodes_matching_letter(placement, 'f')
self.assertEqual(len(nodes), 1)
f_node = nodes[0]
self.assertEqual(f_node.letter, 'f')
self.assertTrue(f_node.placed)
