code: def forward_chainerx(self, inputs):
      (x,) = inputs
      y = chainerx.erf(x)
      return (y,)
  
imports: import chainer
  import chainerx
  import numpy
  from chainerx_tests import math_utils
  from chainerx_tests import op_utils
label_desc: Use image node_id 3 for calling the TestErf obj's underlying member method code with example usage: obj.forward_chainerx(inputs) and returns: y