Update tests for managed memory DLPack device classification

- Fix test_buffer_dunder_dlpack_device_success to expect kDLCUDAManaged
  for unified memory instead of the old buggy kDLCUDAHost.
- Fix test_buffer_dlpack_failure_clean_up error message to match the
  unified classify_dl_device error.
- Add test_managed_buffer_dlpack_roundtrip_device_type to cover the
  Buffer -> DLPack capsule -> StridedMemoryView end-to-end path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rparolin

cuda_core/tests/test_memory.py

@@ -556,7 +556,7 @@ def test_buffer_dunder_dlpack():
     [
         (DummyDeviceMemoryResource, (DLDeviceType.kDLCUDA, 0)),
         (DummyHostMemoryResource, (DLDeviceType.kDLCPU, 0)),
-        (DummyUnifiedMemoryResource, (DLDeviceType.kDLCUDAHost, 0)),
+        (DummyUnifiedMemoryResource, (DLDeviceType.kDLCUDAManaged, 0)),
         (DummyPinnedMemoryResource, (DLDeviceType.kDLCUDAHost, 0)),
     ],
 )
@@ -579,7 +579,7 @@ def test_buffer_dlpack_failure_clean_up():
     dummy_mr = NullMemoryResource()
     buffer = dummy_mr.allocate(size=1024)
     before = sys.getrefcount(buffer)
-    with pytest.raises(BufferError, match="invalid buffer"):
+    with pytest.raises(BufferError, match="buffer is neither device-accessible nor host-accessible"):
         buffer.__dlpack__()
     after = sys.getrefcount(buffer)
     # we use the buffer refcount as sentinel for proper clean-up here,
@@ -588,6 +588,23 @@ def test_buffer_dlpack_failure_clean_up():
     assert after == before
 
 
+def test_managed_buffer_dlpack_roundtrip_device_type():
+    """Verify that a managed Buffer round-trips through DLPack with kDLCUDAManaged."""
+    device = Device()
+    device.set_current()
+    skip_if_managed_memory_unsupported(device)
+    mr = DummyUnifiedMemoryResource(device)
+    buf = mr.allocate(size=1024)
+
+    # Buffer-level classification should report managed.
+    assert buf.__dlpack_device__() == (DLDeviceType.kDLCUDAManaged, 0)
+
+    # The end-to-end path: Buffer -> DLPack capsule -> StridedMemoryView
+    # must preserve kDLCUDAManaged rather than downgrading to kDLCUDAHost.
+    view = StridedMemoryView.from_any_interface(buf, stream_ptr=-1)
+    assert view.__dlpack_device__() == (int(DLDeviceType.kDLCUDAManaged), 0)
+
+
 @pytest.mark.parametrize("use_device_object", [True, False])
 def test_device_memory_resource_initialization(use_device_object):
     """Test that DeviceMemoryResource can be initialized successfully.