it works

ttt/game.py

@@ -58,4 +58,17 @@ class TTTGame:
 
     def check_winner(self, state, symbol):
         "Checks whether the player with `symbol` has won the game."
+        winner = [
+            (0,1,2),
+            (3,4,5),
+            (6,7,8),
+            (0,3,6),
+            (1,4,7),
+            (2,5,8),
+            (0,4,8),
+            (2,4,6)]
+        for combo in winner:
+            if  state["board"][combo[0]] == symbol:
+                if state["board"][combo[0]] == state["board"][combo[1]] == state["board"][combo[2]]:
+                    return True
         return False