code: def test_calculate_population_energies(self):
      # if popsize is 3 then the overall generation has size (6,)
      solver = DifferentialEvolutionSolver(
          rosen, self.bounds, popsize=3
      )
      solver._calculate_population_energies(solver.population)
      solver._promote_lowest_energy()
      assert_equal(np.argmin(solver.population_energies), 0)
  
      # initial calculation of the energies should require 6 nfev.
      assert_equal(solver._nfev, 6)
  
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 28 for calling the TestDifferentialEvolutionSolver obj's underlying member method code with example usage: obj.test_calculate_population_energies() without return types