class_docstr: Tests for integration with the PassthruQNode
docstr: Test that the device probability can be differentiated
docstr_tok: ["Test","that","the","device","probability","can","be","differentiated"]
code: def test_prob_differentiability(self, decorator, interface, tol):
      """Test that the device probability can be differentiated"""
      dev = qml.device("default.mixed", wires=2)
  
      @decorator
      @qml.qnode(dev, diff_method="backprop", interface=interface)
      def circuit(a, b):
          qml.RX(a, wires=0)
          qml.RY(b, wires=1)
          qml.CNOT(wires=[0, 1])
          return qml.probs(wires=[1])
  
      a = tf.Variable(0.54, trainable=True)
      b = tf.Variable(0.12, trainable=True)
  
      with tf.GradientTape() as tape:
          prob_wire_1 = circuit(a, b)
          res = prob_wire_1[1] - prob_wire_1[0]
  
      expected = -np.cos(a) * np.cos(b)
      assert np.allclose(res, expected, atol=tol, rtol=0)
  
      grad = tape.gradient(res, [a, b])
      expected = [np.sin(a) * np.cos(b), np.cos(a) * np.sin(b)]
      assert np.allclose(grad, expected, atol=tol, rtol=0)
  
imports: import pytest
  import numpy
  import pennylane
  from pennylane import numpy
  from pennylane.devices.default_mixed import DefaultMixed
label_desc: Use image node_id 7 for calling the TestPassthruIntegration obj's underlying member method code with example usage: obj.test_prob_differentiability(decorator, interface, tol) and returns: qml