class_docstr: Test the core functionality of the VQE module
class_docstr_tok: ["Test","the","core","functionality","of","the","VQE","module"]
docstr: Test that the gradient of ExpvalCost is accessible and correct when using observable
  optimization and the autograd interface.
docstr_tok: ["Test","that","the","gradient","of","ExpvalCost","is","accessible","and","correct","when","using","observable","optimization","and","the","autograd","interface","."]
code: def test_optimize_grad(self):
      """Test that the gradient of ExpvalCost is accessible and correct when using observable
      optimization and the autograd interface."""
      dev = qml.device("default.qubit", wires=4)
  
      hamiltonian1 = copy.copy(big_hamiltonian)
      hamiltonian2 = copy.copy(big_hamiltonian)
  
      cost = catch_warn_ExpvalCost(
          qml.templates.StronglyEntanglingLayers,
          hamiltonian1,
          dev,
          optimize=True,
          diff_method="parameter-shift",
      )
      cost2 = catch_warn_ExpvalCost(
          qml.templates.StronglyEntanglingLayers,
          hamiltonian2,
          dev,
          optimize=False,
          diff_method="parameter-shift",
      )
  
      np.random.seed(1967)
      shape = qml.templates.StronglyEntanglingLayers.shape(
          n_layers=2, n_wires=4
      )
      w = pnp.random.uniform(
          low=0, high=2 * np.pi, size=shape, requires_grad=True
      )
  
      with qml.Tracker(dev) as tracker:
          dc = qml.grad(cost)(w)
      exec_opt = tracker.totals["executions"]
  
      with tracker:
          dc2 = qml.grad(cost2)(w)
      exec_no_opt = tracker.totals["executions"]
  
      assert exec_no_opt > exec_opt
      assert np.allclose(dc, big_hamiltonian_grad)
      assert np.allclose(dc2, big_hamiltonian_grad)
  
imports: import copy
  import numpy
  import pytest
  import pennylane
  from pennylane import numpy
label_desc: Use image node_id 11 for calling the TestVQE obj's underlying member method code with example usage: obj.test_optimize_grad() without return types