Move test, sort whatsnew

doc/source/whatsnew/v3.0.0.rst

@@ -332,6 +332,7 @@ Performance improvements
 - Performance improvement in :meth:`Index.take` when ``indices`` is a full range indexer from zero to length of index (:issue:`56806`)
 - Performance improvement in :meth:`Index.to_frame` returning a :class:`RangeIndex` columns of a :class:`Index` when possible. (:issue:`58018`)
 - Performance improvement in :meth:`MultiIndex.equals` for equal length indexes (:issue:`56990`)
+- Performance improvement in :meth:`MultiIndex.memory_usage` to ignore the index engine when it isn't already cached. (:issue:`58385`)
 - Performance improvement in :meth:`RangeIndex.__getitem__` with a boolean mask or integers returning a :class:`RangeIndex` instead of a :class:`Index` when possible. (:issue:`57588`)
 - Performance improvement in :meth:`RangeIndex.append` when appending the same index (:issue:`57252`)
 - Performance improvement in :meth:`RangeIndex.argmin` and :meth:`RangeIndex.argmax` (:issue:`57823`)
@@ -345,7 +346,6 @@ Performance improvements
 - Performance improvement in ``DataFrameGroupBy.__len__`` and ``SeriesGroupBy.__len__`` (:issue:`57595`)
 - Performance improvement in indexing operations for string dtypes (:issue:`56997`)
 - Performance improvement in unary methods on a :class:`RangeIndex` returning a :class:`RangeIndex` instead of a :class:`Index` when possible. (:issue:`57825`)
-- Performance improvement in :meth:`MultiIndex.memory_usage` to ignore the index engine when it isn't already cached. (:issue:`58385`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_300.bug_fixes:

pandas/tests/base/test_misc.py

@@ -142,31 +142,6 @@ def test_memory_usage_components_narrow_series(any_real_numpy_dtype):
     assert total_usage == non_index_usage + index_usage
 
 
-def test_memory_usage_doesnt_trigger_engine(index):
-    index._cache.clear()
-    assert "_engine" not in index._cache
-
-    res_without_engine = index.memory_usage()
-    assert "_engine" not in index._cache
-
-    # explicitly load and cache the engine
-    _ = index._engine
-    assert "_engine" in index._cache
-
-    res_with_engine = index.memory_usage()
-
-    # the engine doesn't affect the result even when initialized with values, because
-    # index._engine.sizeof() doesn't consider the content of index._engine.values
-    assert res_with_engine == res_without_engine
-
-    if len(index) == 0:
-        assert res_without_engine == 0
-        assert res_with_engine == 0
-    else:
-        assert res_without_engine > 0
-        assert res_with_engine > 0
-
-
 def test_searchsorted(request, index_or_series_obj):
     # numpy.searchsorted calls obj.searchsorted under the hood.
     # See gh-12238

pandas/tests/indexes/test_old_base.py

@@ -326,6 +326,30 @@ def test_memory_usage(self, index):
         if index.inferred_type == "object":
             assert result3 > result2
 
+    def test_memory_usage_doesnt_trigger_engine(self, index):
+        index._cache.clear()
+        assert "_engine" not in index._cache
+
+        res_without_engine = index.memory_usage()
+        assert "_engine" not in index._cache
+
+        # explicitly load and cache the engine
+        _ = index._engine
+        assert "_engine" in index._cache
+
+        res_with_engine = index.memory_usage()
+
+        # the empty engine doesn't affect the result even when initialized with values,
+        # because engine.sizeof() doesn't consider the content of engine.values
+        assert res_with_engine == res_without_engine
+
+        if len(index) == 0:
+            assert res_without_engine == 0
+            assert res_with_engine == 0
+        else:
+            assert res_without_engine > 0
+            assert res_with_engine > 0
+
     def test_argsort(self, index):
         if isinstance(index, CategoricalIndex):
             pytest.skip(f"{type(self).__name__} separately tested")