class_docstr: Test tensor expectation values
class_docstr_tok: ["Test","tensor","expectation","values"]
docstr: Test that a tensor product involving qml.Projector works correctly
code: def test_projector(self, device, tol, skip_if):
      """Test that a tensor product involving qml.Projector works correctly"""
      n_wires = 3
      dev = device(n_wires)
  
      if "Projector" not in dev.observables:
          pytest.skip(
              "Skipped because device does not support the Projector observable."
          )
  
      skip_if(dev, {"supports_tensor_observables": False})
  
      theta = 0.732
      phi = 0.523
      varphi = -0.543
  
      @qml.qnode(dev)
      def circuit(state):
          qml.RX(theta, wires=[0])
          qml.RX(phi, wires=[1])
          qml.RX(varphi, wires=[2])
          qml.CNOT(wires=[0, 1])
          qml.CNOT(wires=[1, 2])
          return qml.expval(
              qml.PauliZ(wires=[0]) @ qml.Projector(state, wires=[1, 2])
          )
  
      basis_state, state_vector = [0, 0], [1, 0, 0, 0]
      expected = (
          np.cos(varphi / 2) * np.cos(phi / 2) * np.cos(theta / 2)
      ) ** 2 - (
          np.cos(varphi / 2) * np.sin(phi / 2) * np.sin(theta / 2)
      ) ** 2
      assert np.allclose(
          circuit(basis_state), expected, atol=tol(dev.shots)
      )
      assert np.allclose(
          circuit(state_vector), expected, atol=tol(dev.shots)
      )
  
      basis_state, state_vector = [0, 1], [0, 1, 0, 0]
      expected = (
          np.sin(varphi / 2) * np.cos(phi / 2) * np.cos(theta / 2)
      ) ** 2 - (
          np.sin(varphi / 2) * np.sin(phi / 2) * np.sin(theta / 2)
      ) ** 2
      assert np.allclose(
          circuit(basis_state), expected, atol=tol(dev.shots)
      )
      assert np.allclose(
          circuit(state_vector), expected, atol=tol(dev.shots)
      )
  
      basis_state, state_vector = [1, 0], [0, 0, 1, 0]
      expected = (
          np.sin(varphi / 2) * np.sin(phi / 2) * np.cos(theta / 2)
      ) ** 2 - (
          np.sin(varphi / 2) * np.cos(phi / 2) * np.sin(theta / 2)
      ) ** 2
      assert np.allclose(
          circuit(basis_state), expected, atol=tol(dev.shots)
      )
      assert np.allclose(
          circuit(state_vector), expected, atol=tol(dev.shots)
      )
  
      basis_state, state_vector = [1, 1], [0, 0, 0, 1]
      expected = (
          np.cos(varphi / 2) * np.sin(phi / 2) * np.cos(theta / 2)
      ) ** 2 - (
          np.cos(varphi / 2) * np.cos(phi / 2) * np.sin(theta / 2)
      ) ** 2
      assert np.allclose(
          circuit(basis_state), expected, atol=tol(dev.shots)
      )
      assert np.allclose(
          circuit(state_vector), expected, atol=tol(dev.shots)
      )
  
imports: import pytest
  from flaky import flaky
  from scipy.sparse import csr_matrix
  import pennylane
  from pennylane import numpy
  from pennylane.measurements import ClassicalShadowMP, MeasurementTransform, SampleMeasurement, SampleMP, StateMeasurement, StateMP
label_desc: Use image node_id 6 for calling the TestTensorExpval obj's underlying member method code with example usage: obj.test_projector(device, tol, skip_if) and returns: qml