Add a check to see if leaves have the right start positions

test/test_diff_parser.py

@@ -41,6 +41,11 @@ def _assert_valid_graph(node):
     try:
         children = node.children
     except AttributeError:
+        previous_leaf = node.get_previous_leaf()
+        if previous_leaf is not None:
+            if previous_leaf.type != 'error_leaf' or previous_leaf.token_type != 'INDENT':
+                assert previous_leaf.end_pos == node.get_start_pos_of_prefix(), \
+                    (previous_leaf, node)
         return
 
     for child in children: