add test to reproduce #1842

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

tokio/src/task/local.rs

@@ -724,4 +724,32 @@ mod tests {
             join2.await.unwrap()
         });
     }
+    #[test]
+    fn drop_cancels_tasks() {
+        // This test reproduces issue #1842
+        use crate::sync::oneshot;
+        use std::time::Duration;
+
+        let mut rt = runtime::Builder::new()
+            .enable_time()
+            .basic_scheduler()
+            .build()
+            .unwrap();
+
+        let (started_tx, started_rx) = oneshot::channel();
+
+        let local = LocalSet::new();
+        local.spawn_local(async move {
+            started_tx.send(()).unwrap();
+            loop {
+                crate::time::delay_for(Duration::from_secs(3600)).await;
+            }
+        });
+
+        local.block_on(&mut rt, async {
+            started_rx.await.unwrap();
+        });
+        drop(local);
+        drop(rt);
+    }
 }