download: Serialise proxy environment tests

In order to ensure that we do not stomp on each other when running
tests in the download crate to verify proxy behaviour, introduce a
Mutex to guard against this.

Signed-off-by: Daniel Silverstone <[email protected]>

download/tests/read-proxy-env.rs

@@ -4,13 +4,19 @@ 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 lazy_static::lazy_static;
 use reqwest::{blocking::Client, Proxy};
 use url::Url;
 
+lazy_static! {
+    static ref SERIALISE_TESTS: Mutex<()> = Mutex::new(());
+}
+
 fn scrub_env() {
     remove_var("http_proxy");
     remove_var("https_proxy");
@@ -26,6 +32,9 @@ fn scrub_env() {
 // Tests for correctly retrieving the proxy (host, port) tuple from $https_proxy
 #[test]
 fn read_basic_proxy_params() {
+    let _guard = SERIALISE_TESTS
+        .lock()
+        .expect("Unable to lock the test guard");
     scrub_env();
     set_var("https_proxy", "http://proxy.example.com:8080");
     let u = Url::parse("https://www.example.org").ok().unwrap();
@@ -39,6 +48,9 @@ fn read_basic_proxy_params() {
 #[test]
 fn socks_proxy_request() {
     static CALL_COUNT: AtomicUsize = AtomicUsize::new(0);
+    let _guard = SERIALISE_TESTS
+        .lock()
+        .expect("Unable to lock the test guard");
 
     scrub_env();
     set_var("all_proxy", "socks5://127.0.0.1:1080");