input: Write a function to create a TicTacToe game in Python. The function should return a class that initializes a 3x3 board, allows for displaying the current state of the board, and checks if the current player has won the game.
  assert TicTacToe().board == [['_', '_', '_'], ['_', '_', '_'], ['_', '_', '_']]
  assert TicTacToe().check_win() == False
  assert TicTacToe().turn == 'x'
output: class TicTacToe:
      def __init__(self):
          self.board = [['_', '_', '_'], ['_', '_', '_'], ['_', '_', '_']]
          self.turn = 'x'
  
      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