How to use the questionary.prompts.common.build_validator function in questionary

def test_validator_bool_function():
    def validate(t):
        return len(t) == 3

    validator = build_validator(validate)
    assert validator.validate(Document("foo")) is None  # should not raise

def test_validator_instance():
    def validate(t):
        return len(t) == 3

    validator = Validator.from_callable(validate)

    validator = build_validator(validator)
    assert validator.validate(Document("foo")) is None  # should not raise

def test_validator_bool_function_fails():
    def validate(t):
        return len(t) == 3

    validator = build_validator(validate)
    with pytest.raises(ValidationError) as e:
        validator.validate(Document("fooooo"))

    assert e.value.message == "invalid input"

if not choices:
        raise ValueError("No choices is given, you should use Text question.")

    merged_style = merge_styles([DEFAULT_STYLE, style])

    def get_prompt_tokens() -> List[Tuple[Text, Text]]:
        return [("class:qmark", qmark), ("class:question", " {} ".format(message))]

    def get_meta_style(meta: Dict[Text, Any]):
        if meta:
            for key in meta:
                meta[key] = HTML("").format(meta[key])

        return meta

    validator = build_validator(validate)

    if completer is None:
        # use the default completer
        completer = WordCompleter(
            choices,
            ignore_case=ignore_case,
            meta_information=get_meta_style(meta_information),
            match_middle=match_middle,
        )

    p = PromptSession(
        get_prompt_tokens,
        style=merged_style,
        completer=completer,
        validator=validator,
        complete_style=complete_style,

returning a boolean, or an class reference to a
                     subclass of the prompt toolkit Validator class.

           qmark: Question prefix displayed in front of the question.
                  By default this is a `?`

           style: A custom color and style for the question parts. You can
                  configure colors as well as font types for different elements.

       Returns:
           Question: Question instance, ready to be prompted (using `.ask()`).
    """

    merged_style = merge_styles([DEFAULT_STYLE, style])

    validator = build_validator(validate)

    def get_prompt_tokens() -> List[Tuple[Text, Text]]:
        return [("class:qmark", qmark), ("class:question", " {} ".format(message))]

    p = PromptSession(
        get_prompt_tokens, style=merged_style, validator=validator, **kwargs
    )
    p.default_buffer.reset(Document(default))

    return Question(p.app)