code: def test_cases(self):
      for constrained, error_variance, unconstrained in self.cases:
          result = tools.unconstrain_stationary_multivariate(
              constrained, error_variance
          )
          assert_allclose(result[0], unconstrained)
  
imports: import pytest
  import numpy
  from numpy.testing import assert_allclose, assert_equal, assert_array_less, assert_array_equal, assert_almost_equal
  import pandas
  from scipy.linalg import solve_discrete_lyapunov
  from statsmodels.tsa.statespace import tools
  from statsmodels.tsa.stattools import acovf
label_desc: Use image node_id 1 for calling the TestUnconstrainStationaryMultivariate obj's underlying member method code with example usage: obj.test_cases() without return types