1 files changed, 20 insertions, 0 deletions
diff --git a/Lib/test/test_fstring.py b/Lib/test/test_fstring.py
index 35a62a0632..b9bede0d9b 100644
--- a/Lib/test/test_fstring.py
+++ b/Lib/test/test_fstring.py
@@ -9,6 +9,7 @@
 
 import ast
 import os
+import re
 import types
 import decimal
 import unittest
@@ -1198,6 +1199,25 @@ non-important content
         with self.assertRaisesRegex(SyntaxError, "f-string: invalid syntax"):
             compile("f'{a $ b}'", "?", "exec")
 
+    def test_with_two_commas_in_format_specifier(self):
+        error_msg = re.escape("Cannot specify ',' with ','.")
+        with self.assertRaisesRegex(ValueError, error_msg):
+            f'{1:,,}'
+
+    def test_with_two_underscore_in_format_specifier(self):
+        error_msg = re.escape("Cannot specify '_' with '_'.")
+        with self.assertRaisesRegex(ValueError, error_msg):
+            f'{1:__}'
+
+    def test_with_a_commas_and_an_underscore_in_format_specifier(self):
+        error_msg = re.escape("Cannot specify both ',' and '_'.")
+        with self.assertRaisesRegex(ValueError, error_msg):
+            f'{1:,_}'
+
+    def test_with_an_underscore_and_a_comma_in_format_specifier(self):
+        error_msg = re.escape("Cannot specify both ',' and '_'.")
+        with self.assertRaisesRegex(ValueError, error_msg):
+            f'{1:,_}'
 
 if __name__ == '__main__':
     unittest.main()