Adds panic test to hashset delay

eth2/utils/hashmap_delay/Cargo.toml

@@ -7,3 +7,6 @@ edition = "2018"
 [dependencies]
 futures = "0.3.4"
 tokio = { version = "0.2.19", features = ["time"] }
+
+[dev-dependencies]
+tokio = { version = "0.2.19", features = ["time", "rt-threaded", "macros"] }

eth2/utils/hashmap_delay/src/hashset_delay.rs

@@ -163,3 +163,30 @@ where
         }
     }
 }
+
+#[cfg(test)]
+
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn should_not_panic() {
+        let key = 2u8;
+
+        let mut map = HashSetDelay::default();
+
+        map.insert(key);
+        map.update_timeout(&key, Duration::from_secs(100));
+
+        let fut = |cx: &mut Context| {
+            let _ = map.poll_next_unpin(cx);
+            let _ = map.poll_next_unpin(cx);
+            Poll::Ready(())
+        };
+
+        future::poll_fn(fut).await;
+
+        map.insert(key);
+        map.update_timeout(&key, Duration::from_secs(100));
+    }
+}