Issue #28385: An error message when non-empty format spec is passed to

object.__format__ now contains the name of actual type.

1 files changed, 9 insertions, 0 deletions

diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index 2224424efb..b396a76a40 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -1416,6 +1416,15 @@ class AssortedBytesTest(unittest.TestCase):
             self.assertEqual(f(b"'"), '''b"'"''') # '''
             self.assertEqual(f(b"'\""), r"""b'\'"'""") # '
 
+    @check_bytes_warnings
+    def test_format(self):
+        for b in b'abc', bytearray(b'abc'):
+            self.assertEqual(format(b), str(b))
+            self.assertEqual(format(b, ''), str(b))
+            with self.assertRaisesRegex(TypeError,
+                                        r'\b%s\b' % re.escape(type(b).__name__)):
+                format(b, 's')
+
     def test_compare_bytes_to_bytearray(self):
         self.assertEqual(b"abc" == bytes(b"abc"), True)
         self.assertEqual(b"ab" != bytes(b"abc"), True)