chore: checkpoint before Python removal

vendor/tower/tests/util/oneshot.rs

@@ -0,0 +1,40 @@
+use std::task::{Context, Poll};
+use std::{future::Future, pin::Pin};
+use tower::util::ServiceExt;
+use tower_service::Service;
+
+#[tokio::test(flavor = "current_thread")]
+async fn service_driven_to_readiness() {
+    // This test ensures that `oneshot` will repeatedly call `poll_ready` until
+    // the service is ready.
+    let _t = super::support::trace_init();
+
+    struct PollMeTwice {
+        ready: bool,
+    }
+    impl Service<()> for PollMeTwice {
+        type Error = ();
+        type Response = ();
+        type Future = Pin<
+            Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send + Sync + 'static>,
+        >;
+
+        fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), ()>> {
+            if self.ready {
+                Poll::Ready(Ok(()))
+            } else {
+                self.ready = true;
+                cx.waker().wake_by_ref();
+                Poll::Pending
+            }
+        }
+
+        fn call(&mut self, _: ()) -> Self::Future {
+            assert!(self.ready, "service not driven to readiness!");
+            Box::pin(async { Ok(()) })
+        }
+    }
+
+    let svc = PollMeTwice { ready: false };
+    svc.oneshot(()).await.unwrap();
+}