You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: unified.rs
    path of file: ./repos/youki/crates/libcgroups/src/v2
    
    the code of the file until where you have to start completion: use std::{collections::HashMap, path::Path};

use super::controller_type::ControllerType;
use crate::common::{self, ControllerOpt, WrappedIoError};

#[derive(thiserror::Error, Debug)]
pub enum V2UnifiedError {
    #[error("io error: {0}")]
    WrappedIo(#[from] WrappedIoError),
    #[error("subsystem {subsystem} is not available: {err}")]
    SubsystemNotAvailable {
        subsystem: String,
        err: WrappedIoError,
    },
}

pub struct Unified {}

impl Unified {
    pub fn apply(
        controller_opt: &ControllerOpt,
        cgroup_path: &Pa
    
    fn test_set_unified_failed_to_write_subsystem_not_enabled() {
        // arrange
        let tmp = tempfile::tempdir().unwrap();

        let unified = {
            let mut u = HashMap::new();
            u.insert(
                "hugetlb.1GB.limit_in_bytes".to_owned(),
                "72348034".to_owned(),
            );
            u.insert("cpu.weight".to_owned(), "5000".to_owned());
            u
        };

        let resources = LinuxResourcesBuilder::default()
            .unified(unified)
            .build()
            .unwrap();

        let controller_opt = ControllerOpt {
            resources: &resources,
            freezer_state: None,
            oom_score_adj: None,
            disable_oom_killer: false,
        };

        // act
        let result = Unified::apply(&controller_opt, tmp.path(), vec![]);

        // assert
        assert!(result.is_err());
    }