1 files changed, 32 insertions, 0 deletions
diff --git a/third_party/rust/futures/tests/stream_unfold.rs b/third_party/rust/futures/tests/stream_unfold.rs
new file mode 100644
index 0000000000..16b10813b1
--- /dev/null
+++ b/third_party/rust/futures/tests/stream_unfold.rs
@@ -0,0 +1,32 @@
+use futures::future;
+use futures::stream;
+use futures_test::future::FutureTestExt;
+use futures_test::{assert_stream_done, assert_stream_next, assert_stream_pending};
+
+#[test]
+fn unfold1() {
+    let mut stream = stream::unfold(0, |state| {
+        if state <= 2 {
+            future::ready(Some((state * 2, state + 1))).pending_once()
+        } else {
+            future::ready(None).pending_once()
+        }
+    });
+
+    // Creates the future with the closure
+    // Not ready (delayed future)
+    assert_stream_pending!(stream);
+    // Future is ready, yields the item
+    assert_stream_next!(stream, 0);
+
+    // Repeat
+    assert_stream_pending!(stream);
+    assert_stream_next!(stream, 2);
+
+    assert_stream_pending!(stream);
+    assert_stream_next!(stream, 4);
+
+    // No more items
+    assert_stream_pending!(stream);
+    assert_stream_done!(stream);
+}