input: Write a function to create a TicTacToe game in Python. The function should define a class TicTacToe with an initialization method, methods to display the board and check for a winning condition, and should handle the turn management. If the given input is valid, the function should return the appropriate output. If the input is invalid, the function should return an error message.
  
  assert TicTacToe().display() == None
  assert TicTacToe().check_win() == False
  assert TicTacToe().turn == 'x'
output: class TicTacToe:
      def __init__(self):
          self.board = [[' ' for _ in range(3)] for _ in range(3)]
          self.turn = 'x'
  
      def display(self):
          for row in self.board:
              print('|'.join(row))
          return None
  
      def check_win(self):
          for row in self.board:
              if row[0] == row[1] == row[2] != ' ':
                  return True
          for col in range(3):
              if self.board[0][col] == self.board[1][col] == self.board[2][col] != ' ':
                  return True
          if self.board[0][0] == self.board[1][1] == self.board[2][2] != ' ':
              return True
          if self.board[0][2] == self.board[1][1] == self.board[2][0] != ' ':
              return True
          return False