code: def test_timegrain_expressions(
      time_grain: str, expected_result: str
  ) -> None:
      """
      DB Eng Specs (pinot): Test time grain expressions
      """
      from superset.db_engine_specs.pinot import PinotEngineSpec as spec
  
      actual = str(
          spec.get_timestamp_expr(
              col=column("col"), pdf=None, time_grain=time_grain
          )
      )
      assert actual == expected_result
  
imports: from unittest import mock
  import pytest
  from sqlalchemy import column
label_desc: Use image node_id 1 for calling a global function with example usage: test_timegrain_expressions(time_grain, expected_result) without return types