code: def test_trend_n_nobs():
      assert add_trend(nobs=100, trend="n").shape == (100, 0)
      assert add_trend(np.empty((100, 2)), trend="n").shape == (100, 2)
  
imports: import numpy
  from numpy.random import RandomState
  from numpy.testing import assert_array_almost_equal, assert_array_equal, assert_equal
  import pandas
  from pandas.testing import assert_frame_equal
  import pytest
  from arch.utility.timeseries import ColumnNameConflict, add_trend
label_desc: Use image node_id 14 for calling a global function with example usage: test_trend_n_nobs() without return types