Test tag user callback with discarded return

cpp/tests/request.cpp

@@ -363,6 +363,49 @@ TEST_P(RequestTest, TagUserCallback)
 
   for (const auto request : requests)
     ASSERT_THAT(request->getStatus(), UCS_OK);
+  for (const auto status : requestStatus)
+    ASSERT_THAT(status, UCS_OK);
+
+  // Assert data correctness
+  ASSERT_THAT(_recv[0], ContainerEq(_send[0]));
+}
+
+TEST_P(RequestTest, TagUserCallbackDiscardReturn)
+{
+  allocate();
+
+  std::vector<ucs_status_t> requestStatus(2, UCS_INPROGRESS);
+
+  auto checkStatus = [&requestStatus](ucs_status_t status, ::ucxx::RequestCallbackUserData data) {
+    auto idx           = *std::static_pointer_cast<size_t>(data);
+    requestStatus[idx] = status;
+  };
+
+  auto checkCompletion = [&requestStatus, this]() {
+    std::vector<size_t> completed(2, 0);
+    while (std::accumulate(completed.begin(), completed.end(), 0) != 2) {
+      _progressWorker();
+      std::transform(
+        requestStatus.begin(), requestStatus.end(), completed.begin(), [](ucs_status_t status) {
+          return status == UCS_INPROGRESS ? 0 : 1;
+        });
+    }
+  };
+
+  auto sendIndex = std::make_shared<size_t>(0u);
+  auto recvIndex = std::make_shared<size_t>(1u);
+
+  // Submit and wait for transfers to complete
+  std::ignore =
+    _ep->tagSend(_sendPtr[0], _messageSize, ucxx::Tag{0}, false, checkStatus, sendIndex);
+  std::ignore = _ep->tagRecv(
+    _recvPtr[0], _messageSize, ucxx::Tag{0}, ucxx::TagMaskFull, false, checkStatus, recvIndex);
+  checkCompletion();
+
+  copyResults();
+
+  for (const auto status : requestStatus)
+    ASSERT_THAT(status, UCS_OK);
 
   // Assert data correctness
   ASSERT_THAT(_recv[0], ContainerEq(_send[0]));