improves env usage in tests (#6680)

Author: elstehle

cub/cub/device/device_topk.cuh

@@ -118,10 +118,13 @@ CUB_RUNTIME_FUNCTION static cudaError_t dispatch_topk_hub(
 //! DeviceTopK can process all of the built-in C++ numeric primitive types (`unsigned char`, `int`, `double`, etc.) as
 //! well as CUDA's `__half`  and `__nv_bfloat16` 16-bit floating-point types.
 //!
-//! Stability
+//! Determinism
 //! ++++++++++++++++++++++++++
 //!
-//! DeviceTopK currently only provides an unstable version.
+//! DeviceTopK currently only supports unordered output, which may be non-deterministic for certain inputs.
+//! That is, if there are multiple items across the k-th position that compare equal, the subset of tied elements that
+//! ends up in the returned top‑k is not uniquely defined and may vary between runs. This behavior has to be explicitly
+//! acknowledged by the user by passing `cuda::execution::determinism::not_guaranteed`.
 //!
 //! Usage Considerations
 //! ++++++++++++++++++++++++++

cub/test/catch2_test_device_topk_keys.cu

@@ -36,7 +36,7 @@ CUB_RUNTIME_FUNCTION static cudaError_t dispatch_topk_keys(
   NumOutItemsT k,
   cudaStream_t stream = 0)
 {
-  auto stream_env = cuda::std::execution::prop{cuda::get_stream_t{}, cuda::stream_ref{stream}};
+  auto stream_env = cuda::stream_ref{stream};
   auto requirements =
     cuda::execution::require(cuda::execution::determinism::not_guaranteed, cuda::execution::output_ordering::unsorted);
 

cub/test/catch2_test_device_topk_pairs.cu

@@ -37,7 +37,7 @@ CUB_RUNTIME_FUNCTION static cudaError_t dispatch_topk_pairs(
   NumOutItemsT k,
   cudaStream_t stream = 0)
 {
-  auto stream_env = cuda::std::execution::prop{cuda::get_stream_t{}, cuda::stream_ref{stream}};
+  auto stream_env = cuda::stream_ref{stream};
   auto requirements =
     cuda::execution::require(cuda::execution::determinism::not_guaranteed, cuda::execution::output_ordering::unsorted);