How to use the ocpp.messages.CallError function in ocpp

def test_creating_exception_from_call_error():
    call_error = CallError(
        unique_id="1337",
        error_code="ProtocolError",
        error_description="Something went wrong",
        error_details="Some details about the error"
    )

    assert call_error.to_exception() == ProtocolError(
        description="Something went wrong",
        details="Some details about the error"
    )

def test_call_error_representation():
    call = CallError(
        unique_id=1,
        error_code="GenericError",
        error_description="Some message",
        error_details={}
    )

    assert str(call) == \
        ""

def test_creating_exception_from_call_error_with_unknown_error_code():
    call_error = CallError(
        unique_id="1337",
        error_code="418",
        error_description="I'm a teapot",
    )

    with pytest.raises(UnknownCallErrorCodeError):
        call_error.to_exception()

def unpack(msg):
    """
    Unpacks a message into either a Call, CallError or CallResult.
    """
    try:
        msg = json.loads(msg)
    except json.JSONDecodeError as e:
        raise FormatViolationError(f'Message is not valid JSON: {e}')

    if not isinstance(msg, list):
        raise ProtocolError("OCPP message hasn't the correct format. It "
                            f"should be a list, but got {type(msg)} instead")

    for cls in [Call, CallResult, CallError]:
        try:
            if msg[0] == cls.message_type_id:
                return cls(*msg[1:])
        except IndexError:
            raise ProtocolError("Message doesn\'t contain MessageTypeID")

    raise PropertyConstraintViolationError(f"MessageTypeId '{msg[0]}' isn't "
                                           "valid")

def create_call_error(self, exception):
        error_code = "InternalError"
        error_description = "An unexpected error occurred."
        error_details = {}

        if isinstance(exception, OCPPError):
            error_code = exception.code
            error_description = exception.description
            error_details = exception.details

        return CallError(
            self.unique_id,
            error_code,
            error_description,
            error_details,
        )