Add small random delay to async test for stress-testing

tests/mod.rs

@@ -97,6 +97,10 @@ async fn heavy_async() {
     for i in 0..100 {
         let client = client.clone();
         tasks.push(tokio::spawn(async move {
+            tokio::time::sleep(tokio::time::Duration::from_millis(
+                rand::random::<u64>() % 100,
+            ))
+            .await;
             let result = client.addition(i, i).await.unwrap();
             assert_eq!(result, i + i);
         }));