How to use the webargs.fields.Field function in webargs

def test_parse_empty_list(parser, web_request):
    web_request.json = {"things": []}
    args = {"things": fields.List(fields.Field())}
    assert parser.parse(args, web_request) == {"things": []}

def test_it_should_return_missing_if_not_present(self):
        field = fields.Field(multiple=False)
        request = make_request()

        result = parser.parse_headers(request, name, field)

        assert result is missing

def test_parse_cookies_called_when_cookies_is_a_location(parse_cookies, web_request):
    field = fields.Field()
    p = Parser()
    p.parse_arg("foo", field, web_request)
    assert parse_cookies.call_count == 0
    p.parse_arg("foo", field, web_request, locations=("cookies",))
    parse_cookies.assert_called()

def echo_file(request):
    args = {"myfile": fields.Field()}
    result = parser.parse(args, request, locations=("files",))
    myfile = result["myfile"]
    content = myfile.read().decode("utf8")
    return json_response({"myfile": content})

def echo_file():
    args = {"myfile": fields.Field()}
    result = parser.parse(args, locations=("files",))
    fp = result["myfile"]
    content = fp.read().decode("utf8")
    return J({"myfile": content})

def echo_file(request):
    args = {"myfile": fields.Field()}
    result = parser.parse(args, request, locations=("files",))
    myfile = result["myfile"]
    content = myfile.file.read().decode("utf8")
    return {"myfile": content}

def test_parse_json_called_by_parse_arg(parse_json, web_request):
    field = fields.Field()
    p = Parser()
    p.parse_arg("foo", field, web_request)
    parse_json.assert_called_with(web_request, "foo", field)

def test_validation_rules_property():
    instance = model()

    for rule in instance.__validation_rules__.items():
        assert isinstance(rule[1], fields.Field)
        if isinstance(rule[1], fields.List):
            assert isinstance(rule[1].container, fields.Field)

def decorator(func):
            task = rpc_task_name or func.__name__
            if task in self._tasks:
                raise FileExistsError(f'Task {task} has already been registered.')

            if len(webargs_args) == 0:
                signature = inspect.Signature.from_callable(func, follow_wrapped=False)
                logger.info(f'Deriving parameters for task {task} from function definition.')
                argmap = {
                    name: value.annotation
                    for name, value in signature.parameters.items()
                    if isinstance(value.annotation, fields.Field)
                }
            elif len(webargs_args) == 1:
                argmap = webargs_args[0]
            else:
                raise TypeError('Only one positional argument (the webargs argmap) allowed.')

            logger.info(f'Installing task {task}.')

            @functools.wraps(func)
            def call_task(*task_args, **task_kwargs):
                nonlocal func, self
                # Drop the first argument, it's the original arguments dict.
                result = func(*task_args[1:], **task_kwargs)
                return self._encode_result_as_json(result) if rpc_encode_as_json else result

            func_webargs = self._arguments_parser.use_kwargs(argmap, **webargs_kwargs)(call_task)

def register_as_task(func):
    parameters = inspect.Signature.from_callable(func, follow_wrapped=False).parameters
    func.rpc_task = {
        'webargs_argmap': {
            name: value.annotation for name, value in parameters.items() if isinstance(value.annotation, fields.Field)
        }
    }

    return func