1 files changed, 16 insertions, 0 deletions
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 32f76a6..46c7833 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -543,6 +543,22 @@ class IOTest(unittest.TestCase):
         with self.open(support.TESTFN, "r") as f:
             self.assertRaises(TypeError, f.readline, 5.3)
 
+    def test_readline_nonsizeable(self):
+        # Issue #30061
+        # Crash when readline() returns an object without __len__
+        class R(self.IOBase):
+            def readline(self):
+                return None
+        self.assertRaises((TypeError, StopIteration), next, R())
+
+    def test_next_nonsizeable(self):
+        # Issue #30061
+        # Crash when __next__() returns an object without __len__
+        class R(self.IOBase):
+            def __next__(self):
+                return None
+        self.assertRaises(TypeError, R().readlines, 1)
+
     def test_raw_bytes_io(self):
         f = self.BytesIO()
         self.write_ops(f)