fix local testing

Author: sfc-gh-aling

src/snowflake/snowpark/mock/_plan.py

@@ -1495,8 +1495,8 @@ def aggregate_by_groups(cur_group: TableEmulator):
     if isinstance(source_plan, Project):
         return TableEmulator(ColumnEmulator(col) for col in source_plan.project_list)
     if isinstance(source_plan, Join):
-        L_expr_to_alias = {}
-        R_expr_to_alias = {}
+        L_expr_to_alias = getattr(source_plan.left, "expr_to_alias", {})
+        R_expr_to_alias = getattr(source_plan.right, "expr_to_alias", {})
         left = execute_mock_plan(source_plan.left, L_expr_to_alias).reset_index(
             drop=True
         )