Support exporting cut values (#9356)

tests/python-gpu/test_from_cupy.py

@@ -1,3 +1,4 @@
+import json
 import sys
 
 import numpy as np
@@ -10,6 +11,16 @@ from test_dmatrix import set_base_margin_info
 
 from xgboost import testing as tm
 
+cupy = pytest.importorskip("cupy")
+
+
+def test_array_interface() -> None:
+    arr = cupy.array([[1, 2, 3, 4], [1, 2, 3, 4]])
+    i_arr = arr.__cuda_array_interface__
+    i_arr = json.loads(json.dumps(i_arr))
+    ret = xgb.core.from_array_interface(i_arr)
+    np.testing.assert_equal(cupy.asnumpy(arr), cupy.asnumpy(ret))
+
 
 def dmatrix_from_cupy(input_type, DMatrixT, missing=np.NAN):
     '''Test constructing DMatrix from cupy'''

tests/python-gpu/test_gpu_updaters.py

@@ -8,7 +8,11 @@ from hypothesis import assume, given, note, settings, strategies
 import xgboost as xgb
 from xgboost import testing as tm
 from xgboost.testing.params import cat_parameter_strategy, hist_parameter_strategy
-from xgboost.testing.updater import check_init_estimation, check_quantile_loss
+from xgboost.testing.updater import (
+    check_get_quantile_cut,
+    check_init_estimation,
+    check_quantile_loss,
+)
 
 sys.path.append("tests/python")
 import test_updaters as test_up
@@ -264,3 +268,7 @@ class TestGPUUpdaters:
             },
             num_boost_round=150,
         )
+
+    @pytest.mark.skipif(**tm.no_cudf())
+    def test_get_quantile_cut(self) -> None:
+        check_get_quantile_cut("gpu_hist")