def test_validate_backprop_method_invalid_device(self):
"""Test that the method for validating the backprop diff method
tape raises an exception if the device does not support backprop."""
dev = qml.device("default.qubit", wires=1)
with pytest.raises(qml.QuantumFunctionError,
match="does not support native computations"):
QNode._validate_backprop_method(dev, None)
def test_validate_backprop_method_invalid_interface(self, monkeypatch):
"""Test that the method for validating the backprop diff method
tape raises an exception if the wrong interface is provided"""
dev = qml.device("default.qubit", wires=1)
test_interface = "something"
monkeypatch.setitem(dev._capabilities, "passthru_interface",
test_interface)
with pytest.raises(qml.QuantumFunctionError,
match=f"when using the {test_interface}"):
QNode._validate_backprop_method(dev, None)
def test_validate_backprop_method(self, monkeypatch):
"""Test that the method for validating the backprop diff method
tape works as expected"""
dev = qml.device("default.qubit", wires=1)
test_interface = "something"
monkeypatch.setitem(dev._capabilities, "passthru_interface",
test_interface)
tape_class, interface, method = QNode._validate_backprop_method(
dev, test_interface)
assert tape_class is QuantumTape
assert method == "backprop"
assert interface == None