code: def test_convergence(self):
      solver = DifferentialEvolutionSolver(
          rosen, self.bounds, tol=0.2, polish=False
      )
      solver.solve()
      assert_(solver.convergence < 0.2)
  
imports: import multiprocessing
  from scipy.optimize import _differentialevolution
  from scipy.optimize._differentialevolution import DifferentialEvolutionSolver
  from scipy.optimize import differential_evolution
  import numpy
  from scipy.optimize import rosen
  from numpy.testing import assert_equal, assert_allclose, assert_almost_equal, assert_string_equal, assert_
  from pytest import raises, warns
label_desc: Use image node_id 30 for calling the TestDifferentialEvolutionSolver obj's underlying member method code with example usage: obj.test_convergence() without return types