[position] Pop captured piece from CapturesList on unmake

position/src/position.rs

@@ -189,7 +189,12 @@ impl Position {
 
         let unmake_result = self.board.unmake_move(&last_move_record);
 
-        if unmake_result.is_err() {
+        if unmake_result.is_ok() {
+            if let Some(capture) = last_move_record.captured_piece {
+                let popped_piece = self.captures.pop(last_move_record.color);
+                debug_assert_eq!(Some(capture), popped_piece);
+            }
+        } else {
             self.moves.push(last_move_record);
         }
 

position/src/position/captures.rs

@@ -17,6 +17,10 @@ impl CapturesList {
         self.0[color as usize].push(piece);
     }
 
+    pub fn pop(&mut self, color: Color) -> Option<Piece> {
+        self.0[color as usize].pop()
+    }
+
     pub fn is_empty(&self) -> bool {
         self.0.iter().all(Vec::is_empty)
     }