[Refactor] Add parser and formatter e2e testing

tests/test_parser_formatter_e2e.py

@@ -0,0 +1,22 @@
+from core.query_formatter import QueryFormatter
+from core.query_parser import QueryParser
+from mo_sql_parsing import parse
+
+formatter = QueryFormatter()
+parser = QueryParser()
+
+def test_basic_e2e():
+    original_sql = """
+        SELECT e.name, d.name as dept_name, COUNT(*) as emp_count
+        FROM employees e JOIN departments d ON e.department_id = d.id
+        WHERE e.salary > 40000 AND e.age < 60
+        GROUP BY d.id, d.name
+        HAVING COUNT(*) > 2
+        ORDER BY dept_name, emp_count DESC
+        LIMIT 10 OFFSET 5
+    """
+    parsed_ast = parser.parse(original_sql)
+    formatted_sql = formatter.format(parsed_ast)
+
+    # test our output is semantically equivalent to input using mo_sql_parsing
+    assert parse(formatted_sql) == parse(original_sql)