code: def assert_last_step(self, env):
      expected = env.next_timestep[0]._replace(
          step_type=environment.StepType.LAST, discount=0.0
      )
      timestep = env.step([mock.sentinel.action])
      self.assert_equal(timestep, [expected])
  
imports: from absl.testing import absltest
  import mock
  import numpy
  from pysc2.env import enums
  from pysc2.env import environment
  from pysc2.env import mock_sc2_env
  from pysc2.env import sc2_env
  from pysc2.lib import features
  from s2clientprotocol import common_pb2
  from s2clientprotocol import raw_pb2
  from s2clientprotocol import sc2api_pb2
label_desc: Use image node_id 6 for calling the _TestMixin obj's underlying member method code with example usage: obj.assert_last_step(env) without return types