gh-158169: Simplify zlib EOF regression test

Author: GruffElixir

Lib/test/test_zlib.py

@@ -823,14 +823,14 @@ def test_decompress_unused_data(self):
                 self.assertEqual(dco.unused_data, remainder)
 
     def test_decompress_unconsumed_tail_after_eof(self):
-        source = bytes(range(256)) * 4
-        remainder = b'extra'
+        source = b'abcdefghijklmnopqrstuvwxyz'
+        remainder = b'0123456789'
         dco = zlib.decompressobj()
-        chunks = [dco.decompress(zlib.compress(source) + remainder, 100)]
-        while not dco.eof:
-            chunks.append(dco.decompress(dco.unconsumed_tail, 100))
+        data = dco.decompress(zlib.compress(source) + remainder, 1)
+        data += dco.decompress(dco.unconsumed_tail)
 
-        self.assertEqual(b''.join(chunks), source)
+        self.assertTrue(dco.eof)
+        self.assertEqual(data, source)
         self.assertEqual(dco.unconsumed_tail, b'')
         self.assertEqual(dco.unused_data, remainder)
 

Misc/NEWS.d/next/Library/2026-09-25-22-15-54.gh-issue-158169.ZlibTail.rst

@@ -1,2 +1,2 @@
-Clear ``Decompress.unconsumed_tail`` once decompression reaches EOF. Trailing
-input is available only through ``Decompress.unused_data``.
+Fix :attr:`zlib.Decompress.unconsumed_tail` duplicating
+:attr:`~zlib.Decompress.unused_data` after end of stream when *max_length* was used.