code: def test_empty_coeff(self):
      process = ArmaProcess()
      assert_equal(process.arcoefs, np.array([]))
      assert_equal(process.macoefs, np.array([]))
  
      process = ArmaProcess([1, -0.8])
      assert_equal(process.arcoefs, np.array([0.8]))
      assert_equal(process.macoefs, np.array([]))
  
      process = ArmaProcess(ma=[1, -0.8])
      assert_equal(process.arcoefs, np.array([]))
      assert_equal(process.macoefs, np.array([-0.8]))
  
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 1 for calling the TestArmaProcess obj's underlying member method code with example usage: obj.test_empty_coeff() without return types