Ensure that SpooledTemporaryFile rolls over in writelines

Author: bertptrs

Lib/test/test_tempfile.py

@@ -1288,6 +1288,18 @@ def test_writelines(self):
         buf = f.read()
         self.assertEqual(buf, b'xyz')
 
+    def test_writelines_rollover(self):
+        # Verify writelines rolls over before exhausting the iterator
+        f = self.do_create(max_size=2)
+
+        def it():
+            yield b'xy'
+            self.assertFalse(f._rolled)
+            yield b'z'
+            self.assertTrue(f._rolled)
+
+        f.writelines(it())
+
     def test_writelines_sequential(self):
         # A SpooledTemporaryFile should hold exactly max_size bytes, and roll
         # over afterward