code: def test_x0(self):
      # smoke test that checks that x0 is usable.
      res = differential_evolution(rosen, self.bounds, x0=[0.2, 0.8])
      assert res.success
  
      # check what happens if some of the x0 lay outside the bounds
      with assert_raises(ValueError):
          differential_evolution(rosen, self.bounds, x0=[0.2, 2.1])
  
imports: import multiprocessing
  import platform
  from scipy.optimize._differentialevolution import DifferentialEvolutionSolver, _ConstraintWrapper
  from scipy.optimize import differential_evolution
  from scipy.optimize._constraints import Bounds, NonlinearConstraint, LinearConstraint
  from scipy.optimize import rosen
  from scipy.sparse import csr_matrix
  from scipy._lib._pep440 import Version
  import numpy
  from numpy.testing import assert_equal, assert_allclose, assert_almost_equal, assert_array_equal, assert_string_equal, assert_, suppress_warnings
  from pytest import raises, warns
  import pytest
label_desc: Use image node_id 34 for calling the TestDifferentialEvolutionSolver obj's underlying member method code with example usage: obj.test_x0() without return types