apacheGH-36449: [CI][Python] Fix GDB tests in test-cuda-python

ci/scripts/cpp_build.sh

@@ -40,6 +40,8 @@ elif [ -x "$(command -v xcrun)" ]; then
   export ARROW_GANDIVA_PC_CXX_FLAGS="-isysroot;$(xcrun --show-sdk-path)"
 fi
 
+# Reduce size of object files and libraries on CI platforms.
+# ARROW_GDB=ON can be used to override this behaviour.
 if [ "${GITHUB_ACTIONS:-false}" = "true" ]; then
   case "$(uname)" in
     Linux|Darwin|MINGW*)

docker-compose.yml

@@ -866,6 +866,7 @@ services:
       ARROW_FILESYSTEM: "ON"
       ARROW_GANDIVA: "OFF"
       ARROW_GCS: "OFF"
+      ARROW_GDB: "ON"  # Override -g1 for test_gdb.py
       ARROW_HDFS: "ON"
       ARROW_JEMALLOC: "ON"
       ARROW_JSON: "ON"

python/pyarrow/tests/test_cuda.py

@@ -349,27 +349,29 @@ def test_HostBuffer(size):
 
 @pytest.mark.parametrize("size", [0, 1, 1000])
 def test_copy_from_to_host(size):
-
     # Create a buffer in host containing range(size)
-    buf = pa.allocate_buffer(size, resizable=True)  # in host
+    dt = np.dtype('uint16')
+    nbytes = size * dt.itemsize
+    buf = pa.allocate_buffer(nbytes, resizable=True)  # in host
     assert isinstance(buf, pa.Buffer)
     assert not isinstance(buf, cuda.CudaBuffer)
-    arr = np.frombuffer(buf, dtype=np.uint8)
+    arr = np.frombuffer(buf, dtype=dt)
     assert arr.size == size
     arr[:] = range(size)
-    arr_ = np.frombuffer(buf, dtype=np.uint8)
+    arr_ = np.frombuffer(buf, dtype=dt)
     np.testing.assert_equal(arr, arr_)
 
-    device_buffer = global_context.new_buffer(size)
+    # Create a device buffer of the same size and copy from host
+    device_buffer = global_context.new_buffer(nbytes)
     assert isinstance(device_buffer, cuda.CudaBuffer)
     assert isinstance(device_buffer, pa.Buffer)
-    assert device_buffer.size == size
+    assert device_buffer.size == nbytes
     assert not device_buffer.is_cpu
+    device_buffer.copy_from_host(buf, position=0, nbytes=nbytes)
 
-    device_buffer.copy_from_host(buf, position=0, nbytes=size)
-
-    buf2 = device_buffer.copy_to_host(position=0, nbytes=size)
-    arr2 = np.frombuffer(buf2, dtype=np.uint8)
+    # Copy back to host and compare contents
+    buf2 = device_buffer.copy_to_host(position=0, nbytes=nbytes)
+    arr2 = np.frombuffer(buf2, dtype=dt)
     np.testing.assert_equal(arr, arr2)