def test_validator_with_underscore_name() -> None:
    """
    https://github.com/pydantic/pydantic/issues/5252
    """

    def f(name: str) -> str:
        return name.lower()

    class Model(BaseModel):
        name: str
        _normalize_name = field_validator('name')(f)

    assert Model(name='Adrian').name == 'adrian'

    https://github.com/pydantic/pydantic/issues/5252
    
tests/test_validators.py