code: def test_flat(self, use_pandas):
      test_data = {
          "x": np.arange(20),
          "y": np.zeros(20),
          "out": np.zeros(20),
      }
      if use_pandas:
          test_data = {k: pd.Series(test_data[k]) for k in test_data}
      expected_lowess = np.array([test_data["x"], test_data["out"]]).T
      actual_lowess = lowess(test_data["y"], test_data["x"])
      assert_almost_equal(expected_lowess, actual_lowess, 7)
  
imports: import os
  import numpy
  from numpy.testing import assert_, assert_allclose, assert_almost_equal, assert_equal, assert_raises
  import pytest
  from statsmodels.nonparametric.smoothers_lowess import lowess
  import pandas
label_desc: Use image node_id 2 for calling the TestLowess obj's underlying member method code with example usage: obj.test_flat(use_pandas) without return types