Optional normalization for learning to rank. (#10094)

tests/python/test_ranking.py

@@ -13,6 +13,7 @@ import xgboost
 from xgboost import testing as tm
 from xgboost.testing.data import RelDataCV, simulate_clicks, sort_ltr_samples
 from xgboost.testing.params import lambdarank_parameter_strategy
+from xgboost.testing.ranking import run_normalization
 
 
 def test_ndcg_custom_gain():
@@ -188,6 +189,10 @@ def test_unbiased() -> None:
     assert df["ti+"].iloc[-1] < df["ti+"].iloc[0]
 
 
+def test_normalization() -> None:
+    run_normalization("cpu")
+
+
 class TestRanking:
     @classmethod
     def setup_class(cls):