code: def test_arma2ar(self):
      process1 = ArmaProcess.from_coeffs([], [0.8])
      vals = process1.arma2ar(100)
      assert_almost_equal(vals, (-0.8) ** np.arange(100.0))
  
imports: from statsmodels.compat.pandas import QUARTER_END
  import datetime
  import numpy
  from numpy.testing import assert_, assert_allclose, assert_almost_equal, assert_array_almost_equal, assert_equal, assert_raises
  import pandas
  import pytest
  from statsmodels.sandbox.tsa.fftarma import ArmaFft
  from statsmodels.tsa.arima.model import ARIMA
  from statsmodels.tsa.arima_process import ArmaProcess, arma_acf, arma_acovf, arma_generate_sample, arma_impulse_response, index2lpol, lpol2index, lpol_fiar, lpol_fima
  from statsmodels.tsa.tests.results import results_arma_acf
  from statsmodels.tsa.tests.results.results_process import armarep
label_desc: Use image node_id 9 for calling the TestArmaProcess obj's underlying member method code with example usage: obj.test_arma2ar() without return types