code: def test_arma_acf():
      # Check for specific AR(1)
      N = 20
      phi = 0.9
      sigma = 1
      # rep 1: from module function
      rep1 = arma_acf([1, -phi], [1], N)
      # rep 2: manually
      acovf = np.array(
          [1.0 * sigma * phi**i / (1 - phi**2) for i in range(N)]
      )
      rep2 = acovf / (1.0 / (1 - phi**2))
      assert_allclose(rep1, rep2)
  
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 3 for calling a global function with example usage: test_arma_acf() without return types