code: def test_builder_to_backend_smoke(self, compute_unit, backend):
      t = np.array(range(4)).reshape(4, 1).astype(np.float32)
      decompressed_constant = (
          np.array([1, 2, 3, 4]).reshape(4, 1).astype(np.float32)
      )
      input_placeholders = {
          "x": mb.placeholder(shape=t.shape),
      }
      input_values = {"x": t}
  
      def build(x):
          lut_data = np.array(
              [
                  -19.0,
                  4.0,
                  0.0,
                  -1.0,
                  1.0,
                  3.0,
                  5.0,
                  -8.0,
                  19,
                  13,
                  42,
                  4.5,
                  5.4,
                  2.0,
                  -6,
                  -7,
              ]
          ).astype(np.float32)
          indices = np.array([212, 21]).astype(np.uint8)
          shape = np.array([4, 1]).astype(np.uint32)
          y = mb.constexpr_lut_to_dense(
              lut=lut_data, indices=indices, shape=shape
          )
          return mb.add(x=x, y=y)
  
      expected_output_types = (4, 1, types.fp32)
      expected_outputs = t + decompressed_constant.astype(np.float32)
  
      mlmodel = run_compare_builder(
          build,
          input_placeholders,
          input_values,
          expected_output_types,
          expected_outputs,
          compute_unit=compute_unit,
          backend=backend,
      )
  
      # validate that the constexpr op is not removed by any graph pass
      prog = mlmodel._mil_program
      assert "constexpr_lut_to_dense" in get_op_types_in_program(prog)
  
imports: import itertools
  import numpy
  import pytest
  from coremltools.converters.mil import testing_reqs
  from coremltools.converters.mil.mil import Builder
  from coremltools.converters.mil.mil import types
  from coremltools.converters.mil.mil.ops.defs.iOS16 import constexpr_ops
  from coremltools.converters.mil.mil.ops.tests.iOS16 import backends
  from coremltools.converters.mil.mil.ops.tests.testing_utils import run_compare_builder
  from coremltools.converters.mil.testing_utils import get_op_types_in_program, ssa_fn
label_desc: Use image node_id 1 for calling the TestConstexprLutToDense obj's underlying member method code with example usage: obj.test_builder_to_backend_smoke(compute_unit, backend) and returns: mb