From 07b4c5adcd60302076f6fdf7709d1c256f8d8e20 Mon Sep 17 00:00:00 2001
From: Thomas Li <47963215+lithomas1@users.noreply.github.com>
Date: Thu, 5 Jan 2023 17:00:45 -0800
Subject: [PATCH 1/3] TST: Test CoW with DataFrame.items()

---
 pandas/tests/copy_view/test_methods.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/pandas/tests/copy_view/test_methods.py b/pandas/tests/copy_view/test_methods.py
index 0ff359061fd67..4f6d109ae673c 100644
--- a/pandas/tests/copy_view/test_methods.py
+++ b/pandas/tests/copy_view/test_methods.py
@@ -634,3 +634,21 @@ def test_droplevel(using_copy_on_write):
 
     assert not np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
     tm.assert_frame_equal(df, df_orig)
+
+
+def test_items(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [7, 8, 9]})
+    df_orig = df.copy()
+    for name, vals in df.items():
+        ser = Series(vals)
+
+        if using_copy_on_write:
+            assert np.shares_memory(ser.values, get_array(df, name))
+        else:
+            assert not np.shares_memory(ser.values, get_array(df, name))
+
+        # mutating df2 triggers a copy-on-write for that column / block
+        ser.iloc[0] = 0
+
+        assert not np.shares_memory(ser.values, get_array(df, name))
+        tm.assert_frame_equal(df, df_orig)

From 00eb76efe02b46000d36beca127265f2765d5113 Mon Sep 17 00:00:00 2001
From: Thomas Li <47963215+lithomas1@users.noreply.github.com>
Date: Sat, 7 Jan 2023 11:42:40 -0800
Subject: [PATCH 2/3] Fix tests

---
 pandas/tests/copy_view/test_methods.py | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/pandas/tests/copy_view/test_methods.py b/pandas/tests/copy_view/test_methods.py
index 4f6d109ae673c..6de91156a4475 100644
--- a/pandas/tests/copy_view/test_methods.py
+++ b/pandas/tests/copy_view/test_methods.py
@@ -642,13 +642,14 @@ def test_items(using_copy_on_write):
     for name, vals in df.items():
         ser = Series(vals)
 
-        if using_copy_on_write:
-            assert np.shares_memory(ser.values, get_array(df, name))
-        else:
-            assert not np.shares_memory(ser.values, get_array(df, name))
+        assert np.shares_memory(ser.values, get_array(df, name))
 
         # mutating df2 triggers a copy-on-write for that column / block
         ser.iloc[0] = 0
 
-        assert not np.shares_memory(ser.values, get_array(df, name))
-        tm.assert_frame_equal(df, df_orig)
+        if using_copy_on_write:
+            assert not np.shares_memory(ser.values, get_array(df, name))
+            tm.assert_frame_equal(df, df_orig)
+        else:
+            # Original frame will be modified
+            assert df.loc[0, name] == 0

From 6566da4866ccd2beba141e33c0ea9ddec1fa4f15 Mon Sep 17 00:00:00 2001
From: Thomas Li <47963215+lithomas1@users.noreply.github.com>
Date: Fri, 20 Jan 2023 09:17:49 -0800
Subject: [PATCH 3/3] update

---
 pandas/tests/copy_view/test_methods.py | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/pandas/tests/copy_view/test_methods.py b/pandas/tests/copy_view/test_methods.py
index a5b43dd5428ca..3479da3475336 100644
--- a/pandas/tests/copy_view/test_methods.py
+++ b/pandas/tests/copy_view/test_methods.py
@@ -994,20 +994,23 @@ def test_squeeze(using_copy_on_write):
 def test_items(using_copy_on_write):
     df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [7, 8, 9]})
     df_orig = df.copy()
-    for name, vals in df.items():
-        ser = Series(vals)
 
-        assert np.shares_memory(ser.values, get_array(df, name))
+    # Test this twice, since the second time, the item cache will be
+    # triggered, and we want to make sure it still works then.
+    for i in range(2):
+        for name, ser in df.items():
 
-        # mutating df2 triggers a copy-on-write for that column / block
-        ser.iloc[0] = 0
+            assert np.shares_memory(get_array(ser, name), get_array(df, name))
 
-        if using_copy_on_write:
-            assert not np.shares_memory(ser.values, get_array(df, name))
-            tm.assert_frame_equal(df, df_orig)
-        else:
-            # Original frame will be modified
-            assert df.loc[0, name] == 0
+            # mutating df triggers a copy-on-write for that column / block
+            ser.iloc[0] = 0
+
+            if using_copy_on_write:
+                assert not np.shares_memory(get_array(ser, name), get_array(df, name))
+                tm.assert_frame_equal(df, df_orig)
+            else:
+                # Original frame will be modified
+                assert df.loc[0, name] == 0
 
 
 @pytest.mark.parametrize(