class_docstr: Tests for the var function
docstr: Test that a UserWarning is raised if the provided
  argument might not be hermitian.
docstr_tok: ["Test","that","a","UserWarning","is","raised","if","the","provided","argument","might","not","be","hermitian","."]
code: def test_not_an_observable(self):
      """Test that a UserWarning is raised if the provided
      argument might not be hermitian."""
      dev = qml.device("default.qubit", wires=2)
  
      @qml.qnode(dev)
      def circuit():
          qml.RX(0.52, wires=0)
          return qml.var(qml.prod(qml.PauliX(0), qml.PauliZ(0)))
  
      with pytest.warns(
          UserWarning, match="Prod might not be hermitian."
      ):
          _ = circuit()
  
file_path: pennylane/tests/measurements/test_var.py
imports: import numpy
  import pytest
  import pennylane
  from pennylane.measurements import Variance, Shots
label_desc: Use image node_id 2 for calling the TestVar obj's underlying member method code with example usage: obj.test_not_an_observable() and returns: qml