class_docstr: Tests for helper functions.
code: def test_process_ids_unknown_arg(self, circuit, enc_args, argnum):
      dev = qml.device("default.qubit", wires=2)
      qnode = qml.QNode(circuit, dev)
      with pytest.raises(ValueError, match="Not all names in"):
          _process_ids(enc_args, argnum, qnode)
  
imports: from collections import OrderedDict
  import numpy
  import pytest
  import pennylane
  from pennylane import numpy
  from pennylane.fourier.qnode_spectrum import _process_ids, qnode_spectrum
  from pennylane.measurements import SampleMP, StateMP, VarianceMP
label_desc: Use image node_id 2 for calling the TestHelpers obj's underlying member method code with example usage: obj.test_process_ids_unknown_arg(circuit, enc_args, argnum) without return types