code: def test_add_time_trend_dataframe(rng):
      n = 10
      x = rng.randn(n, 1)
      x = pd.DataFrame(x, columns=["col1"])
      trend_1 = add_trend(x, trend="t")
      assert_array_almost_equal(
          np.asarray(trend_1["trend"]), np.arange(1.0, n + 1)
      )
  
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 4 for calling a global function with example usage: test_add_time_trend_dataframe(rng) without return types