code: def test_ar1_forecast_simulation_one(self):
      # Bug found when simulation=1
      am = arch_model(self.ar1, mean="AR", vol="GARCH", lags=[1])
      res = am.fit(disp="off")
      forecast = res.forecast(
          horizon=10, method="simulation", simulations=1
      )
      assert forecast.simulations.variances.shape == (1, 1, 10)
  
imports: import datetime
  from itertools import product
  import numpy
  from numpy.random import RandomState
  from numpy.testing import assert_allclose
  import pandas
  from pandas.testing import assert_frame_equal
  import pytest
  from arch.data import sp500
  from arch.tests.univariate.test_variance_forecasting import preserved_state
  from arch.univariate import APARCH, ARX, EGARCH, FIGARCH, GARCH, HARCH, HARX, ConstantMean, ConstantVariance, EWMAVariance, MIDASHyperbolic, RiskMetrics2006, ZeroMean, arch_model
  from arch.univariate.mean import _ar_forecast, _ar_to_impulse
label_desc: Use image node_id 12 for calling the TestForecasting obj's underlying member method code with example usage: obj.test_ar1_forecast_simulation_one() without return types