code: def test_mean_field_warn(backend):
      def model():
          x = pyro.sample("x", dist.Normal(0.0, 1.0))
          pyro.sample("y", dist.Normal(x, 1.0))
  
      def guide():
          loc = pyro.param("loc", torch.tensor(0.0))
          y = pyro.sample("y", dist.Normal(loc, 1.0))
          pyro.sample("x", dist.Normal(y, 1.0))
  
      with pyro_backend(backend):
          elbo = infer.TraceMeanField_ELBO()
          assert_warning(model, guide, elbo)
  
imports: import warnings
  import pytest
  import funsor
  from funsor.testing import xfail_param
  from funsor.util import get_backend
label_desc: Use image node_id 17 for calling a global function with example usage: test_mean_field_warn(backend) without return types