test(download): fix clippy warnings regarding Mutex in async

download/tests/read-proxy-env.rs

@@ -4,15 +4,16 @@ use std::env::{remove_var, set_var};
 use std::error::Error;
 use std::net::TcpListener;
 use std::sync::atomic::{AtomicUsize, Ordering};
-use std::sync::Mutex;
 use std::thread;
 use std::time::Duration;
 
 use env_proxy::for_url;
+use once_cell::sync::Lazy;
 use reqwest::{Client, Proxy};
+use tokio::sync::Mutex;
 use url::Url;
 
-static SERIALISE_TESTS: Mutex<()> = Mutex::new(());
+static SERIALISE_TESTS: Lazy<Mutex<()>> = Lazy::new(|| Mutex::new(()));
 
 fn scrub_env() {
     remove_var("http_proxy");
@@ -29,9 +30,7 @@ fn scrub_env() {
 // Tests for correctly retrieving the proxy (host, port) tuple from $https_proxy
 #[tokio::test]
 async fn read_basic_proxy_params() {
-    let _guard = SERIALISE_TESTS
-        .lock()
-        .expect("Unable to lock the test guard");
+    let _guard = SERIALISE_TESTS.lock().await;
     scrub_env();
     set_var("https_proxy", "http://proxy.example.com:8080");
     let u = Url::parse("https://www.example.org").ok().unwrap();
@@ -45,9 +44,7 @@ async fn read_basic_proxy_params() {
 #[tokio::test]
 async fn socks_proxy_request() {
     static CALL_COUNT: AtomicUsize = AtomicUsize::new(0);
-    let _guard = SERIALISE_TESTS
-        .lock()
-        .expect("Unable to lock the test guard");
+    let _guard = SERIALISE_TESTS.lock().await;
 
     scrub_env();
     set_var("all_proxy", "socks5://127.0.0.1:1080");