add test for depr. attibute added to deprecation list

Author: tp

doc/source/whatsnew/v0.23.1.txt

@@ -44,6 +44,8 @@ Documentation Changes
 Bug Fixes
 ~~~~~~~~~
 
+- tab completion on :class:`Index` in IPython no longer shows out deprecation warnings (:issue:`21125`)
+
 Groupby/Resample/Rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^
 

pandas/tests/indexes/test_base.py

@@ -2088,6 +2088,17 @@ def test_get_duplicates_deprecated(self):
         with tm.assert_produces_warning(FutureWarning):
             index.get_duplicates()
 
+    def test_tab_complete_warning(self, ip):
+        # https://github.com/pandas-dev/pandas/issues/16409
+        pytest.importorskip('IPython', minversion="6.0.0")
+        from IPython.core.completer import provisionalcompleter
+
+        code = "import pandas as pd; idx = pd.Index([1, 2])"
+        ip.run_code(code)
+        with tm.assert_produces_warning(None):
+            with provisionalcompleter('ignore'):
+                list(ip.Completer.completions('idx.', 4))
+
 
 class TestMixedIntIndex(Base):
     # Mostly the tests from common.py for which the results differ