gh-94808: Cover %p in PyUnicode_FromFormat (#96677)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Lib/test/test_unicode.py

@@ -2807,6 +2807,25 @@ class CAPITest(unittest.TestCase):
         check_format('repr=abc',
                      b'repr=%V', 'abc', b'xyz')
 
+        # test %p
+        # We cannot test the exact result,
+        # because it returns a hex representation of a C pointer,
+        # which is going to be different each time. But, we can test the format.
+        p_format_regex = r'^0x[a-zA-Z0-9]{8,}$'
+        p_format1 = PyUnicode_FromFormat(b'%p', 'abc')
+        self.assertIsInstance(p_format1, str)
+        self.assertRegex(p_format1, p_format_regex)
+
+        p_format2 = PyUnicode_FromFormat(b'%p %p', '123456', b'xyz')
+        self.assertIsInstance(p_format2, str)
+        self.assertRegex(p_format2,
+                         r'0x[a-zA-Z0-9]{8,} 0x[a-zA-Z0-9]{8,}')
+
+        # Extra args are ignored:
+        p_format3 = PyUnicode_FromFormat(b'%p', '123456', None, b'xyz')
+        self.assertIsInstance(p_format3, str)
+        self.assertRegex(p_format3, p_format_regex)
+
         # Test string decode from parameter of %s using utf-8.
         # b'\xe4\xba\xba\xe6\xb0\x91' is utf-8 encoded byte sequence of
         # '\u4eba\u6c11'