code: def test_default_trend():
      # Test that we are setting the trend default correctly
      endog = dta["infl"].iloc[:50]
  
      # Defaults when only endog is specified
      mod = ARIMA(endog)
      # with no integration, default trend a constant
      assert_equal(mod._spec_arima.trend_order, 0)
      assert_allclose(mod.exog, np.ones((mod.nobs, 1)))
  
      # Defaults with integrated model
      mod = ARIMA(endog, order=(0, 1, 0))
      # with no integration, default trend is none
      assert_equal(mod._spec_arima.trend_order, None)
      assert_equal(mod.exog, None)
  
imports: from statsmodels.compat.platform import PLATFORM_WIN32
  import io
  import numpy
  import pandas
  import pytest
  from numpy.testing import assert_equal, assert_allclose, assert_raises, assert_
  from statsmodels.datasets import macrodata
  from statsmodels.tsa.arima.model import ARIMA
  from statsmodels.tsa.arima.estimators.yule_walker import yule_walker
  from statsmodels.tsa.arima.estimators.burg import burg
  from statsmodels.tsa.arima.estimators.hannan_rissanen import hannan_rissanen
  from statsmodels.tsa.arima.estimators.innovations import innovations, innovations_mle
  from statsmodels.tsa.arima.estimators.statespace import statespace
label_desc: Use image node_id 1 for calling a global function with example usage: test_default_trend() without return types