code: def test_to_datetime():
      """Checks to_datetime functionality is as expected."""
  
      df = pd.DataFrame(
          {"date1": ["20190101", "20190102", "20190304", np.nan]}
      ).to_datetime("date1", format="%Y%m%d")
      assert df["date1"].dtype == np.dtype("datetime64[ns]")
      assert df["date1"].iloc[0].isoformat() == "2019-01-01T00:00:00"
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_to_datetime() without return types