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: wait_for_load.rs
    path of file: ./repos/amethyst/amethyst_test/src
    
    the code of the file until where you have to start completion: use std::time::Duration;

use amethyst::{assets::ProgressCounter, core::Stopwatch, ecs::World, State, StateData, Trans};
use derivative::Derivative;
use log::warn;

use crate::GameUpdate;

/// Time limit before outputting a warning message.
const LOADING_TIME_LIMIT: Duration = Duration::from_secs(10);

/// Reads a `ProgressCounter` resource and waits for it to be `complete()`.
#[derive(Derivative)]
#[derivative(Debug)]
pub struct WaitForLoad {
    /// Tracks how long the `WaitForLoad` state has run.
    ///
    /// Used t
    
    fn uses_custom_completion_function() -> Result<(), Error> {
        AmethystApplication::blank()
            .with_system(Processor::<TestAsset>::new(), "test_asset_processor", &[])
            .with_effect(|world| {
                let mut in_memory_source = InMemorySource::new();
                in_memory_source.insert(String::from("file.ron"), b"(val: 123)".to_vec());

                let mut loader = world.write_resource::<DefaultLoader>();
                loader.add_source(IN_MEMORY_SOURCE_ID, in_memory_source);
            })
            .with_effect(|world| {
                let mut progress_counter = ProgressCounter::new();
                let test_asset_handle = {
                    let loader = data.resources.get::<DefaultLoader>().unwrap();
                    loader.load_from(
                        "file.ron",
                        RonFormat,
                        IN_MEMORY_SOURCE_ID,
                        &mut progress_counter,
                        &world.read_resource::<AssetStorage<TestAsset>>(),
                    )
                };

                world.insert(test_asset_handle);
                world.insert(vec![progress_counter]);
            })
            .with_state(|| {
                WaitForLoad::new_with_fn(|world| {
                    world
                        .read_resource::<Vec<ProgressCounter>>()
                        .first()
                        .expect("Expected `Vec<ProgressCounter>` with one element.")
                        .is_complete()
                })
            })
            .with_assertion(|world| {
                let test_asset_handle = world.read_resource::<Handle<TestAsset>>();
                let test_assets = world.read_resource::<AssetStorage<TestAsset>>();
                let test_asset = test_assets
                    .get(&test_asset_handle)
                    .expect("Expected `TestAsset` to be loaded.");

                assert_eq!(&TestAsset { val: 123 }, test_asset);
            })
            .run()
    }