input: Write a function to implement a TicTacToe game in Python. The function should include an initialization method that sets up the game board and a method to display the current state of the board. Additionally, a method should be provided to check if the current player has won the game. The function should also include assert statements to test the functionality of the TicTacToe game.
  assert TicTacToe().check_win() == False
  assert TicTacToe().display() == None
  assert TicTacToe().board == [['_', '_', '_'], ['_', '_', '_'], ['_', '_', '_']]
output: def __init__(self):
      self.board = [['_' for _ in range(3)] for _ in range(3)]
  
  def display(self):
      for row in self.board:
          print(" ".join(row))
  
  def check_win(self):
      for row in self.board:
          if row[0] == row[1] == row[2] and row[0] != '_':
              return True
      for col in range(3):
          if self.board[0][col] == self.board[1][col] == self.board[2][col] and self.board[0][col] != '_':
              return True
      if self.board[0][0] == self.board[1][1] == self.board[2][2] and self.board[0][0] != '_':
          return True
      if self.board[0][2] == self.board[1][1] == self.board[2][0] and self.board[0][2] != '_':
          return True
      return False