text: """Test for modify_params_after_iter/info_hook"""
  import io
  import contextlib
  
  import numpy as np
  
  import krotov
  
  from test_objectives import transmon_ham_and_states
  
  
  def test_infohook_chaining(transmon_ham_and_states):
      """Test that transmon_ham_and_states and info_hooks get chained together
      correctly. This tests a whole bunch of implementation details:
  
      - return values from multiple info_hooks combine in tuple
      - return value None (from modify_params_after_iter) gets ignored
      - shared_data gets passed along through multiple hooks
      - shared_data is cleared in each iteration
      """
      H, psi0, psi1 = transmon_ham_and_states
      obj = krotov.Objective(initial_state=psi0, target=psi1, H=H)
      tlist = np.array([0, 0.01, 0.02])
      pulse_options = {H[1][1]: krotov.PulseOptions(1.0)}
      stdout = io.StringIO()
  
      def adjust_lambda_a(**args):
          λₐ = args['lambda_vals'][0]
          args['lambda_vals'][0] *= 0.5
          if 'messages' not in args['shared_data']:
              args['shared_data']['messages'] = []
          args['shared_data']['messages'].append(
              'λₐ: %s → %s' % (λₐ, args['lambda_vals'][0])
          )
  
      def print_fidelity(**args):
          F_re = np.average(np.array(args['tau_vals']).real)
          print("Iteration %d: \tF = %f" % (args['iteration'], F_re))
          return F_re
  
      def print_messages(**args):
          if 'messages' in args['shared_data']:
              message = "; ".join(
                  [msg for msg in args['shared_data']['messages']]
              )
              print("\tmsg: " + message)
              return message
  
      with contextlib.redirect_stdout(stdout):
          oct_result = krotov.optimize_pulses(
              [obj],
              pulse_options=pulse_options,
              tlist=tlist,
              propagator=krotov.propagators.expm,
              chi_constructor=krotov.functionals.chis_re,
              info_hook=krotov.info_hooks.chain(print_fidelity, print_messages),
              modify_params_after_iter=adjust_lambda_a,
              iter_stop=2,
          )
  
      assert len(oct_result.info_vals) == 3
      assert isinstance(oct_result.info_vals[1], tuple)
      assert len(oct_result.info_vals[1]) == 2
      assert abs(oct_result.info_vals[1][0] - 0.001978333994757067) < 1e-8
      assert oct_result.info_vals[1][1] == 'λₐ: 0.5 → 0.25'
      assert 'Iteration 0: \tF = 0.000000' in stdout.getvalue()
      assert 'msg: λₐ: 1.0 → 0.5' in stdout.getvalue()
      assert 'Iteration 1: \tF = 0.001978' in stdout.getvalue()
      assert 'msg: λₐ: 0.5 → 0.25' in stdout.getvalue()
  