code: def test_is_valid():
      # Additional tests for the `is_valid` property (tests for NaN checks were
      # already done in `test_set_params_single`).
      spec = specification.SARIMAXSpecification(
          order=(1, 1, 1),
          seasonal_order=(1, 1, 1, 4),
          enforce_stationarity=True,
          enforce_invertibility=True,
      )
      p = params.SARIMAXParams(spec=spec)
  
      # Doesn't start out as valid
      assert_(not p.is_valid)
      # Given stationary / invertible values, it is valid
      p.params = [0.5, 0.5, 0.5, 0.5, 1.0]
      assert_(p.is_valid)
      # With either non-stationary or non-invertible values, not valid
      p.params = [1.0, 0.5, 0.5, 0.5, 1.0]
      assert_(not p.is_valid)
      p.params = [0.5, 1.0, 0.5, 0.5, 1.0]
      assert_(not p.is_valid)
      p.params = [0.5, 0.5, 1.0, 0.5, 1.0]
      assert_(not p.is_valid)
      p.params = [0.5, 0.5, 0.5, 1.0, 1.0]
      assert_(not p.is_valid)
  
file_path: statsmodels/statsmodels/tsa/arima/tests/test_params.py
imports: import numpy
  import pandas
  from numpy.testing import assert_, assert_equal, assert_allclose, assert_raises
  from statsmodels.tsa.arima import specification, params
label_desc: Use image node_id 10 for calling a global function with example usage: test_is_valid() without return types