code: def test_diff_timedelta(self, unit):
      # GH#4533
      df = DataFrame(
          {
              "time": [
                  Timestamp("20130101 9:01"),
                  Timestamp("20130101 9:02"),
              ],
              "value": [1.0, 2.0],
          }
      )
      df["time"] = df["time"].dt.as_unit(unit)
  
      res = df.diff()
      exp = DataFrame(
          [[pd.NaT, np.nan], [pd.Timedelta("00:01:00"), 1]],
          columns=["time", "value"],
      )
      exp["time"] = exp["time"].dt.as_unit(unit)
      tm.assert_frame_equal(res, exp)
  
imports: import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Series, Timestamp, date_range
  import pandas._testing
label_desc: Use image node_id 11 for calling the TestDataFrameDiff obj's underlying member method code with example usage: obj.test_diff_timedelta(unit) without return types