diff --git a/azlite_portfolio_clean.py b/azlite_portfolio_clean.py
index 67a4835..2c0f5b1 100644
--- a/azlite_portfolio_clean.py
+++ b/azlite_portfolio_clean.py
@@ -24,6 +24,14 @@
 import torch.nn as nn
 import torch.optim as optim
 
+
+# ----------------------------- Constant ---------------------------------------
+PROMOTION_MAP = {
+    chess.QUEEN: 1,
+    chess.ROOK: 2,
+    chess.BISHOP: 3,
+    chess.KNIGHT: 4,
+}
 # ----------------------------- Config ---------------------------------------
 
 DEVICE = torch.device("cuda" if torch.cuda.is_available() else "cpu")
@@ -241,9 +249,7 @@ def run(
                 if mv.promotion is None:
                     promo_idxs.append(0)
                 else:
-                    promo_map = {chess.QUEEN: 1, chess.ROOK: 2,
-                                 chess.BISHOP: 3, chess.KNIGHT: 4}
-                    promo_idxs.append(promo_map.get(mv.promotion, 0))
+                    promo_idxs.append(PROMOTION_MAP.get(mv.promotion, 0))
             from_idx_t = torch.tensor(
                 from_idxs, dtype=torch.long, device=DEVICE)
             to_idx_t = torch.tensor(to_idxs, dtype=torch.long, device=DEVICE)
@@ -338,9 +344,8 @@ def _simulate(self, board: chess.Board, root: MCTSNode) -> float:
                         if mv.promotion is None:
                             promo_idxs.append(0)
                         else:
-                            promo_map = {chess.QUEEN: 1, chess.ROOK: 2,
-                                         chess.BISHOP: 3, chess.KNIGHT: 4}
-                            promo_idxs.append(promo_map.get(mv.promotion, 0))
+                            PROMOTION_MAP.get(mv.promotion, 0)
+                            promo_idxs.append(PROMOTION_MAP.get(mv.promotion, 0))
                     logits = self.net.score_moves(
                         state_embed.squeeze(0),
                         torch.tensor(from_idxs, dtype=torch.long,
@@ -434,16 +439,11 @@ def self_play_episode(mcts: MCTS, max_moves: int = SELFPLAY_MAX_MOVES,
         arr_state = board_to_tensor(board)
         from_idxs = [mv.from_square for mv in legal]
         to_idxs = [mv.to_square for mv in legal]
-        promo_map = {
-            chess.QUEEN: 1,
-            chess.ROOK: 2,
-            chess.BISHOP: 3,
-            chess.KNIGHT: 4,
-        }
+
         promo_idxs = [
-            0 if mv.promotion is None else promo_map.get(mv.promotion, 0)
+            0 if mv.promotion is None else PROMOTION_MAP.get(mv.promotion, 0)
             for mv in legal
-        ]
+            ]
         examples.append(
             SelfPlayExample(
                 state=arr_state,
diff --git a/tests/test_promotion_mapping.py b/tests/test_promotion_mapping.py
new file mode 100644
index 0000000..37c2b39
--- /dev/null
+++ b/tests/test_promotion_mapping.py
@@ -0,0 +1,61 @@
+import sys
+import os
+
+# Add parent directory to Python path so azlite_portfolio_clean can be imported
+sys.path.append(os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+
+import chess
+import numpy as np
+from azlite_portfolio_clean import PROMOTION_MAP, self_play_episode
+
+def test_promotion_map_constant():
+    """Test that PROMOTION_MAP constant exists and has correct values"""
+    # Test the constant exists and has expected structure
+    assert PROMOTION_MAP is not None
+    assert isinstance(PROMOTION_MAP, dict)
+    assert len(PROMOTION_MAP) == 4
+    
+    # Test specific mappings
+    assert PROMOTION_MAP[chess.QUEEN] == 1
+    assert PROMOTION_MAP[chess.ROOK] == 2
+    assert PROMOTION_MAP[chess.BISHOP] == 3
+    assert PROMOTION_MAP[chess.KNIGHT] == 4
+
+def test_promotion_map_values():
+    """Test that PROMOTION_MAP has correct chess piece mappings"""
+    expected = {
+        chess.QUEEN: 1,
+        chess.ROOK: 2,
+        chess.BISHOP: 3,
+        chess.KNIGHT: 4,
+    }
+    assert PROMOTION_MAP == expected
+
+def test_promotion_map_usage():
+    """Test that the promotion mapping logic works correctly"""
+    
+    assert PROMOTION_MAP.get(chess.QUEEN, 0) == 1
+    assert PROMOTION_MAP.get(chess.ROOK, 0) == 2
+    assert PROMOTION_MAP.get(chess.BISHOP, 0) == 3
+    assert PROMOTION_MAP.get(chess.KNIGHT, 0) == 4
+    assert PROMOTION_MAP.get(None, 0) == 0  
+
+def test_promotion_indices_logic():
+    """Test the promotion index calculation logic from self_play_episode"""
+    
+    mock_moves = [
+        type('MockMove', (), {'promotion': chess.QUEEN})(),
+        type('MockMove', (), {'promotion': chess.ROOK})(),
+        type('MockMove', (), {'promotion': chess.BISHOP})(),
+        type('MockMove', (), {'promotion': chess.KNIGHT})(),
+        type('MockMove', (), {'promotion': None})(),  
+    ]
+    
+   
+    promo_idxs = [
+        0 if mv.promotion is None else PROMOTION_MAP.get(mv.promotion, 0)
+        for mv in mock_moves
+    ]
+    
+    expected = [1, 2, 3, 4, 0]  # Queen, Rook, Bishop, Knight, None
+    assert promo_idxs == expected
\ No newline at end of file