code: def test_errors():
      n = 100
      with pytest.raises(ValueError):
          add_trend(x=None, trend="unknown", nobs=n)
      with pytest.raises(ValueError):
          add_trend(x=None, trend="ct")
      x = np.ones((100, 1))
      with pytest.raises(ValueError):
          add_trend(x, trend="ct", has_constant="raise")
  
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 13 for calling a global function with example usage: test_errors() without return types