code: def test_pval_extremes():
      assert phillips_ouliaris_pval(3.0, "Zt", "n", 2) == 1.0
      np.testing.assert_allclose(
          phillips_ouliaris_pval(2.1, "Zt", "n", 2), 0.996850543
      )
      assert phillips_ouliaris_pval(-3000.0, "Zt", "n", 2) == 0.0
      # Above and below tau-star
      above = phillips_ouliaris_pval(1.0, "Zt", "n", 2)
      below = phillips_ouliaris_pval(0.0, "Zt", "n", 2)
      assert above > below
  
file_path: arch/arch/tests/unitroot/test_phillips_ouliaris.py
imports: import numpy
  from numpy.testing import assert_allclose
  import pytest
  from statsmodels.iolib.summary import Summary
  from arch.typing import Float64Array, UnitRootTrend
  from arch.unitroot._phillips_ouliaris import CriticalValueWarning, phillips_ouliaris_cv, phillips_ouliaris_pval
  from arch.unitroot.cointegration import phillips_ouliaris
  from arch.utility.timeseries import add_trend
label_desc: Use image node_id 9 for calling a global function with example usage: test_pval_extremes() without return types