code: def test_erf_value_inference(self):
      INPUT_SIZE = (2, 3, 4)
      rs = np.random.RandomState(1234)
      x = rs.random(INPUT_SIZE)
  
      @mb.program(input_specs=[])
      def prog():
          return mb.erf(x=x)
  
      ops = list(prog.functions.values())[0].operations
      assert len(ops) == 2
      assert ops[0].op_type == "const"
      erf_op = ops[1]
      assert erf_op.op_type == "erf"
      np.testing.assert_allclose(
          erf_op.value_inference(),
          scipy.special.erf(x),
          atol=1e-04,
          rtol=1e-05,
      )
  
imports: import itertools
  import numpy
  import pytest
  import scipy
  from coremltools.converters.mil.mil import Builder
  from coremltools.converters.mil.mil import Function, get_new_symbol, types
  from coremltools.converters.mil.mil.ops.tests.iOS14 import backends
  from coremltools.converters.mil.mil.ops.tests.testing_utils import run_compare_builder
  from coremltools.converters.mil.mil.types.symbolic import is_compatible_symbolic_vector
  from coremltools.converters.mil.testing_reqs import compute_units
  from coremltools.converters.mil.testing_utils import ssa_fn
label_desc: Use image node_id 31 for calling the TestElementwiseUnary obj's underlying member method code with example usage: obj.test_erf_value_inference() and returns: mb