[3.12] gh-107735: Add C API tests for PySys_GetObject() and PySys_SetObject() (GH-107736) (#107740)

[3.12] gh-107735: Add C API tests for PySys_GetObject() and PySys_SetObject() (GH-107736).
(cherry picked from commit bea5f93196)

Lib/test/test_capi/test_misc.py

@@ -51,6 +51,8 @@ _testcapi = import_helper.import_module('_testcapi')
 import _testinternalcapi
 
 
+NULL = None
+
 def decode_stderr(err):
     return err.decode('utf-8', 'replace').replace('\r', '')
 
@@ -1121,6 +1123,46 @@ class CAPITest(unittest.TestCase):
         del d.extra
         self.assertIsNone(d.extra)
 
+    def test_sys_getobject(self):
+        getobject = _testcapi.sys_getobject
+
+        self.assertIs(getobject(b'stdout'), sys.stdout)
+        with support.swap_attr(sys, '\U0001f40d', 42):
+            self.assertEqual(getobject('\U0001f40d'.encode()), 42)
+
+        self.assertIs(getobject(b'nonexisting'), AttributeError)
+        self.assertIs(getobject(b'\xff'), AttributeError)
+        # CRASHES getobject(NULL)
+
+    def test_sys_setobject(self):
+        setobject = _testcapi.sys_setobject
+
+        value = ['value']
+        value2 = ['value2']
+        try:
+            self.assertEqual(setobject(b'newattr', value), 0)
+            self.assertIs(sys.newattr, value)
+            self.assertEqual(setobject(b'newattr', value2), 0)
+            self.assertIs(sys.newattr, value2)
+            self.assertEqual(setobject(b'newattr', NULL), 0)
+            self.assertFalse(hasattr(sys, 'newattr'))
+            self.assertEqual(setobject(b'newattr', NULL), 0)
+        finally:
+            with contextlib.suppress(AttributeError):
+                del sys.newattr
+        try:
+            self.assertEqual(setobject('\U0001f40d'.encode(), value), 0)
+            self.assertIs(getattr(sys, '\U0001f40d'), value)
+            self.assertEqual(setobject('\U0001f40d'.encode(), NULL), 0)
+            self.assertFalse(hasattr(sys, '\U0001f40d'))
+        finally:
+            with contextlib.suppress(AttributeError):
+                delattr(sys, '\U0001f40d')
+
+        with self.assertRaises(UnicodeDecodeError):
+            setobject(b'\xff', value)
+        # CRASHES setobject(NULL, value)
+
 
 @requires_limited_api
 class TestHeapTypeRelative(unittest.TestCase):