[Breaking] Remove num roots. (#5059)

tests/python/test_basic.py

@@ -231,7 +231,6 @@ class TestBasic(unittest.TestCase):
         assert output == solution
 
 
-
 class TestBasicPathLike(unittest.TestCase):
     """Unit tests using the os_fspath and pathlib.Path for file interaction."""
 

tests/python/test_dmatrix.py

@@ -63,11 +63,11 @@ class TestDMatrix(unittest.TestCase):
         # Sliced UInt array
         z = np.array([12, 34, 56], np.uint32)[::2]
         dmat = xgb.DMatrix(np.array([[]]))
-        dmat.set_uint_info('root_index', z)
-        from_view = dmat.get_uint_info('root_index')
+        dmat.set_uint_info('group', z)
+        from_view = dmat.get_uint_info('group_ptr')
         dmat = xgb.DMatrix(np.array([[]]))
-        dmat.set_uint_info('root_index', z + 0)
-        from_array = dmat.get_uint_info('root_index')
+        dmat.set_uint_info('group', z + 0)
+        from_array = dmat.get_uint_info('group_ptr')
         assert (from_view.shape == from_array.shape)
         assert (from_view == from_array).all()
 
@@ -142,7 +142,7 @@ class TestDMatrix(unittest.TestCase):
         dtrain.get_float_info('label')
         dtrain.get_float_info('weight')
         dtrain.get_float_info('base_margin')
-        dtrain.get_uint_info('root_index')
+        dtrain.get_uint_info('group_ptr')
 
     def test_sparse_dmatrix_csr(self):
         nrow = 100

tests/python/test_ranking.py

@@ -161,8 +161,6 @@ class TestRanking(unittest.TestCase):
         """
         Retrieve the group number from the dmatrix
         """
-        # control that should work
-        self.dtrain.get_uint_info('root_index')
         # test the new getter
         self.dtrain.get_uint_info('group_ptr')