Debugging a stack level too deep error - Ruby - ruby

Question

I am building a Tic Tac Toe game in which the user can play a computer, or computers can play each other. While building the AI I am running into the below error. How can I debug this? I understand it is to do with a loop somewhere but I can't find it.
ttt-with-ai-project-cb-000/lib/players/computer.rb:13:in `each': stack level too deep (SystemStackError)
from ttt-with-ai-project-cb-000/lib/players/computer.rb:13:in `detect'
from ttt-with-ai-project-cb-000/lib/players/computer.rb:13:in `check_move'
from ttt-with-ai-project-cb-000/lib/players/computer.rb:8:in `move'
from ttt-with-ai-project-cb-000/lib/game.rb:61:in `wargame_turn'
from ttt-with-ai-project-cb-000/lib/game.rb:64:in `wargame_turn'
from ttt-with-ai-project-cb-000/lib/game.rb:64:in `wargame_turn'
from ttt-with-ai-project-cb-000/lib/game.rb:64:in `wargame_turn'
from ttt-with-ai-project-cb-000/lib/game.rb:64:in `wargame_turn'
... 11900 levels...
from bin/tictactoe:37:in `block in run_game'
from bin/tictactoe:35:in `times'
from bin/tictactoe:35:in `run_game'
from bin/tictactoe:79:in `<main>'
The Offending Methods
lib/players/computer.rb
def move(board)
check_move(board)
end
def check_move(board)
win_combo = Game::WIN_COMBINATIONS.detect do |indices|
board.cells[indices[0]] == token && board.cells[indices[1]] == token || board.cells[indices[1]] == token && board.cells[indices[2]] == token || board.cells[indices[0]] == token && board.cells[indices[2]] == token
end
win_combo.detect {|index| board.cells[index] == " "}.join if win_combo
end
lib/game.rb
def wargame_turn
input = current_player.move(board)
if !board.valid_move?(input)
wargame_turn
else
board.update(input, current_player)
end
end
bin/tictactoe calls the method in the following block within #run_game:
100.times do
game = Game.new(Players::Computer.new("X"), player_2 = Players::Computer.new("O"))
game.wargames
if game.winner == "X"
x_wins += 1
elsif game.winner == "O"
x_wins += 1
elsif game.draw?
draws += 1
end
end

Answer 1

You can use the ruby Tracer class:
ruby -r tracer your_main_script.rb
Also, you can take a look at your code and see where the loop may happen:
def wargame_turn
input = current_player.move(board)
if !board.valid_move?(input)
wargame_turn #### HERE'S A POTENTIAL INFINITE LOOP
So the heart of the problem seems at:
if !board.valid_move?(input)
It could be a good start.