TST: df.loc[:, 'col'] returning a view, but df.loc[df.index, 'col'] returning a copy (#34996)

Author: arw2019

pandas/tests/indexing/test_loc.py

@@ -894,6 +894,22 @@ def test_identity_slice_returns_new_object(self):
         original_series[:3] = [7, 8, 9]
         assert all(sliced_series[:3] == [7, 8, 9])
 
+    def test_loc_copy_vs_view(self):
+        # GH 15631
+        x = DataFrame(zip(range(3), range(3)), columns=["a", "b"])
+
+        y = x.copy()
+        q = y.loc[:, "a"]
+        q += 2
+
+        tm.assert_frame_equal(x, y)
+
+        z = x.copy()
+        q = z.loc[x.index, "a"]
+        q += 2
+
+        tm.assert_frame_equal(x, z)
+
     def test_loc_uint64(self):
         # GH20722
         # Test whether loc accept uint64 max value as index.