better error msg

Author: kevinjqliu

tests/table/test_init.py

@@ -1158,6 +1158,9 @@ def test_serialize_commit_table_request() -> None:
 
 def test_table_update_have_corresponding_dispatch() -> None:
     from pyiceberg.table import TableUpdate, _apply_table_update
-    # every TableUpdate should have a corresponding `_apply_table_update` dispatch function
 
-    assert len(_apply_table_update.registry) == len(TableUpdate.__origin__.__args__)  # type: ignore
+    # every TableUpdate class should have corresponding `_apply_table_update` dispatch function
+    table_update_class = set(TableUpdate.__origin__.__args__)  # type: ignore
+    dispatch_function_class = set(_apply_table_update.registry.keys())
+    missing_dispatch_function = table_update_class - dispatch_function_class
+    assert len(missing_dispatch_function) == 0, f"Missing dispatch function for {missing_dispatch_function}"