gh-100871: Improve `copy` module tests (GH-100872)

CC @AlexWaygood as the reviewer of https://github.com/python/cpython/pull/100818

Automerge-Triggered-By: GH:AlexWaygood

Lib/test/test_copy.py

@@ -51,6 +51,9 @@ class TestCopy(unittest.TestCase):
         self.assertRaises(TypeError, copy.copy, x)
         copyreg.pickle(C, pickle_C, C)
         y = copy.copy(x)
+        self.assertIsNot(x, y)
+        self.assertEqual(type(y), C)
+        self.assertEqual(y.foo, x.foo)
 
     def test_copy_reduce_ex(self):
         class C(object):
@@ -311,6 +314,9 @@ class TestCopy(unittest.TestCase):
         self.assertRaises(TypeError, copy.deepcopy, x)
         copyreg.pickle(C, pickle_C, C)
         y = copy.deepcopy(x)
+        self.assertIsNot(x, y)
+        self.assertEqual(type(y), C)
+        self.assertEqual(y.foo, x.foo)
 
     def test_deepcopy_reduce_ex(self):
         class C(object):
@@ -352,8 +358,8 @@ class TestCopy(unittest.TestCase):
             pass
         def f():
             pass
-        tests = [None, 42, 2**100, 3.14, True, False, 1j,
-                 "hello", "hello\u1234", f.__code__,
+        tests = [None, ..., NotImplemented, 42, 2**100, 3.14, True, False, 1j,
+                 b"bytes", "hello", "hello\u1234", f.__code__,
                  NewStyle, range(10), max, property()]
         for x in tests:
             self.assertIs(copy.deepcopy(x), x)

Lib/test/test_slice.py

@@ -5,6 +5,7 @@ import operator
 import sys
 import unittest
 import weakref
+import copy
 
 from pickle import loads, dumps
 from test import support
@@ -244,6 +245,41 @@ class SliceTest(unittest.TestCase):
             self.assertEqual(s.indices(15), t.indices(15))
             self.assertNotEqual(id(s), id(t))
 
+    def test_copy(self):
+        s = slice(1, 10)
+        c = copy.copy(s)
+        self.assertIs(s, c)
+
+        s = slice(1, 10, 2)
+        c = copy.copy(s)
+        self.assertIs(s, c)
+
+        # Corner case for mutable indices:
+        s = slice([1, 2], [3, 4], [5, 6])
+        c = copy.copy(s)
+        self.assertIs(s, c)
+        self.assertIs(s.start, c.start)
+        self.assertIs(s.stop, c.stop)
+        self.assertIs(s.step, c.step)
+
+    def test_deepcopy(self):
+        s = slice(1, 10)
+        c = copy.deepcopy(s)
+        self.assertEqual(s, c)
+
+        s = slice(1, 10, 2)
+        c = copy.deepcopy(s)
+        self.assertEqual(s, c)
+
+        # Corner case for mutable indices:
+        s = slice([1, 2], [3, 4], [5, 6])
+        c = copy.deepcopy(s)
+        self.assertIsNot(s, c)
+        self.assertEqual(s, c)
+        self.assertIsNot(s.start, c.start)
+        self.assertIsNot(s.stop, c.stop)
+        self.assertIsNot(s.step, c.step)
+
     def test_cycle(self):
         class myobj(): pass
         o = myobj()