Fix fen loading tests

binding/python_c_ffi.py

@@ -92,6 +92,14 @@ def sq(name):
     return f + 8 * r
 
 
+def popcount(x):
+    return x.bit_count()
+
+
+def get_rank_mask(rank):
+    return sum(1 << (rank*8 + f) for f in range(8))
+
+
 class ChessFFI:
     def __init__(self):
         self.lib_path = "./build/libchess.so"
@@ -130,10 +138,6 @@ class ChessFFI:
 
     def attackers_to(self, board, sq, by):
         return self._c_attackers_to(board, sq, by)
-
-
-    def popcount(self, x):
-        return x.bit_count()
     
 
     def _load_lib(self):