class_docstr: Tests for helper functions.
code: def test_process_ids_index_error(self):
      dev = qml.device("default.qubit", wires=2)
      qnode = qml.QNode(circuit_0, dev)
      with pytest.raises(IndexError, match="x"):
          _process_ids(None, [5], 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 3 for calling the TestHelpers obj's underlying member method code with example usage: obj.test_process_ids_index_error() without return types