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: integration_tests.rs
    path of file: ./repos/vector/src/sinks/splunk_hec/logs
    
    the code of the file until where you have to start completion: use std::{convert::TryFrom, iter, num::NonZeroU8};

use chrono::{TimeZone, Timelike, Utc};
use futures::{future::ready, stream};
use serde_json::Value as JsonValue;
use tokio::time::{sleep, Duration};
use vector_lib::codecs::{JsonSerializerConfig, TextSerializerConfig};
use vector_lib::lookup::lookup_v2::{ConfigValuePath, OptionalTargetPath};
use vector_lib::{
    
    
async fn splunk_insert_index() {
    let cx = SinkContext::default();

    let mut config = config(TextSerializerConfig::default().into(), vec![]).await;
    config.index = Template::try_from("custom_index".to_string()).ok();
    let (sink, _) = config.build(cx).await.unwrap();

    let message = random_string(100);
    let event = LogEvent::from(message.clone());
    run_and_assert_sink_compliance(sink, stream::once(ready(event)), &HTTP_SINK_TAGS).await;

    let entry = find_entry(message.as_str()).await;

    assert_eq!(entry["index"].as_str().unwrap(), "custom_index");
}