def test_validate_backprop_finite_shots(self, device_string):
"""Test that a device with finite shots cannot be used with backpropagation."""
dev = qml.device(device_string, wires=1, shots=100)
with pytest.raises(qml.QuantumFunctionError,
match=r"Backpropagation is only supported"):
QNode._validate_backprop_method(dev, "autograd")
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.gaussian", 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_child_method_wrong_interface(self, monkeypatch):
"""Test that the method for validating the backprop diff method
tape raises an error if a child device supports backprop but using a different interface"""
dev = qml.device("default.qubit", wires=1)
test_interface = "something"
orig_capabilities = dev.capabilities().copy()
orig_capabilities["passthru_devices"] = {test_interface: "default.gaussian"}
monkeypatch.setattr(dev, "capabilities", lambda: orig_capabilities)
with pytest.raises(qml.QuantumFunctionError, match=r"when using the \['something'\] interface"):
QNode._validate_backprop_method(dev, "another_interface")
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)
method, diff_options, device = QNode._validate_backprop_method(dev, "something")
assert method == "backprop"
assert device is dev
def test_validate_backprop_child_method(self, monkeypatch):
"""Test that the method for validating the backprop diff method
tape works as expected if a child device supports backprop"""
dev = qml.device("default.qubit", wires=1)
test_interface = "something"
orig_capabilities = dev.capabilities().copy()
orig_capabilities["passthru_devices"] = {test_interface: "default.gaussian"}
monkeypatch.setattr(dev, "capabilities", lambda: orig_capabilities)
method, diff_options, device = QNode._validate_backprop_method(dev, test_interface)
assert method == "backprop"
assert isinstance(device, qml.devices.DefaultGaussian)
