better comments and tests

Author: topper-123

pandas/core/indexes/multi.py

@@ -994,10 +994,10 @@ def _shallow_copy(self, values=None, **kwargs):
             return MultiIndex.from_tuples(values, names=names, **kwargs)
 
         result = self.copy(**kwargs)
-        cache = self._cache.copy()
-        if "levels" in cache:
-            cache["levels"] = FrozenList(lev._shallow_copy() for lev in cache["levels"])
-        result._cache = cache
+        result._cache = self._cache.copy()
+        # GH32669
+        if "levels" in result._cache:
+            del result._cache["levels"]
         return result
 
     def _shallow_copy_with_infer(self, values, **kwargs):

pandas/tests/indexes/common.py

@@ -923,11 +923,12 @@ def test_contains_requires_hashable_raises(self):
     def test_shallow_copy_copies_cache(self):
         # GH32669
         idx = self.create_index()
-        idx.get_loc(idx[0])  # initiate the _engine etc.
+        idx.get_loc(idx[0])  # populates the _cache.
         shallow_copy = idx._shallow_copy()
+
         # check that the shallow_copied cache is a copy of the original
         assert idx._cache == shallow_copy._cache
         assert idx._cache is not shallow_copy._cache
-        # the cache values should reference the same objects
+        # cache values should reference the same object
         for key, val in idx._cache.items():
-            assert shallow_copy._cache[key] is val
+            assert shallow_copy._cache[key] is val, key

pandas/tests/indexes/multi/test_names.py

@@ -7,7 +7,6 @@
 
 def check_level_names(index, names):
     assert [level.name for level in index.levels] == list(names)
-    assert index.names == list(names)
 
 
 def test_slice_keep_name():