Backported test for issue #20238.
diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index 49469fd..8767d51 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -657,6 +657,12 @@
tar.addfile(tarfile.TarInfo("foo"))
tar.close()
self.assertTrue(fobj.closed is False, "external fileobjs must never closed")
+ # Issue #20238: Incomplete gzip output with mode="w:gz"
+ data = fobj.getvalue()
+ del tar
+ test_support.gc_collect()
+ self.assertFalse(fobj.closed)
+ self.assertEqual(data, fobj.getvalue())
class WriteTest(WriteTestBase):