Add test that catches EventReader + drain failure observed in example

Fails on line 467, after we try again

Author: alice-i-cecile

crates/bevy_ecs/src/event.rs

@@ -445,6 +445,29 @@ mod tests {
         assert!(current_events.events_a.is_empty());
     }
 
+    #[test]
+    fn write_eat_repeat() {
+        struct E;
+        let mut events = Events::<E>::default();
+        let mut reader = events.get_reader();
+
+        assert!(reader.iter(&events).next().is_none());
+
+        // Send an event
+        events.send(E);
+        assert!(reader.iter(&events).next().is_some());
+        assert!(reader.iter(&events).next().is_none());
+
+        // Eat all events
+        let _ = events.drain();
+        assert!(reader.iter(&events).next().is_none());
+
+        // Try again
+        events.send(E);
+        assert!(reader.iter(&events).next().is_some());
+        assert!(reader.iter(&events).next().is_none());
+    }
+
     #[test]
     fn test_events() {
         let mut events = Events::<TestEvent>::default();