Add example failing test

futures/tests/stream.rs

@@ -1,5 +1,9 @@
+use std::cell::Cell;
 use std::iter;
+use std::pin::Pin;
+use std::rc::Rc;
 use std::sync::Arc;
+use std::task::Context;
 
 use futures::channel::mpsc;
 use futures::executor::block_on;
@@ -9,6 +13,7 @@ use futures::sink::SinkExt;
 use futures::stream::{self, StreamExt};
 use futures::task::Poll;
 use futures::{ready, FutureExt};
+use futures_core::Stream;
 use futures_test::task::noop_context;
 
 #[test]
@@ -436,3 +441,38 @@ fn ready_chunks() {
         assert_eq!(s.next().await.unwrap(), vec![4]);
     });
 }
+
+struct SlowStream {
+    times_should_poll: usize,
+    times_polled: Rc<Cell<usize>>,
+}
+impl Stream for SlowStream {
+    type Item = usize;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        self.times_polled.set(self.times_polled.get() + 1);
+        if self.times_polled.get() % 2 == 0 {
+            cx.waker().wake_by_ref();
+            return Poll::Pending;
+        }
+        if self.times_polled.get() == self.times_should_poll {
+            return Poll::Ready(None);
+        }
+        Poll::Ready(Some(self.times_polled.get()))
+    }
+}
+
+#[test]
+fn select_with_strategy_doesnt_terminate_early() {
+    let times_should_poll = 10;
+    let count = Rc::new(Cell::new(0));
+    let b = stream::iter([10, 20]);
+
+    let selected = stream::select_with_strategy(
+        SlowStream { times_should_poll, times_polled: count.clone() },
+        b,
+        |_: &mut ()| stream::PollNext::Left,
+    );
+    block_on(selected.for_each(|v| async move { println!("{}", v) }));
+    assert_eq!(count.get(), times_should_poll);
+}