code: def test_return_multitrace(self, simple_model, discard_warmup):
      with simple_model:
          mtrace = pm.sample(
              trace=mcb.NumPyBackend(),
              tune=5,
              draws=7,
              cores=1,
              chains=3,
              step=pm.Metropolis(),
              discard_tuned_samples=discard_warmup,
              return_inferencedata=False,
          )
      assert isinstance(mtrace, pm.backends.base.MultiTrace)
      tune = mtrace._straces[0].get_sampler_stats("tune")
      assert isinstance(tune, np.ndarray)
      if discard_warmup:
          assert tune.shape == (7, 3)
      else:
          assert tune.shape == (12, 3)
      pass
  
imports: import logging
  import arviz
  import numpy
  import pytest
  import pymc
  from pymc.backends import init_traces
  from pymc.step_methods.arraystep import ArrayStepShared
  from pymc.backends.mcbackend import ChainRecordAdapter, find_data, get_variables_and_point_fn, make_runmeta_and_point_fn
label_desc: Use image node_id 1 for calling the TestMcBackendSampling obj's underlying member method code with example usage: obj.test_return_multitrace(simple_model, discard_warmup) without return types