Issue #8681: Make the zlib module's error messages more informative when
the zlib itself doesn't give any detailed explanation.
diff --git a/Lib/test/test_zlib.py b/Lib/test/test_zlib.py
index 2fc4313..cbc3ed4 100644
--- a/Lib/test/test_zlib.py
+++ b/Lib/test/test_zlib.py
@@ -135,6 +135,13 @@
         x = zlib.compress(data)
         self.assertEqual(zlib.decompress(x), data)
 
+    def test_incomplete_stream(self):
+        # An useful error message is given
+        x = zlib.compress(HAMLET_SCENE)
+        self.assertRaisesRegexp(zlib.error,
+            "Error -5 while decompressing data: incomplete or truncated stream",
+            zlib.decompress, x[:-1])
+
     # Memory use of the following functions takes into account overallocation
 
     @precisionbigmemtest(size=_1G + 1024 * 1024, memuse=3)