Index: Lib/test/test_imaplib.py
===================================================================
--- Lib/test/test_imaplib.py	(revision 71980)
+++ Lib/test/test_imaplib.py	(working copy)
@@ -4,8 +4,23 @@
 from test import test_support
 import unittest
 
+class DummyIMAP(imaplib.IMAP4):
+    def __init__(self):
+        """Skip connections, for testing."""
+        pass
 
+    def _simple_command(self, name, *args):
+        """Return self.literal, for testing methods affecting literal."""
+        return self.literal
+
 class TestImaplib(unittest.TestCase):
+    # CR, LF in literal should not be replaced by CRLF, issue 5430
+    def test_cr_lf_literal_preservation(self):
+        i = DummyIMAP()
+        teststr = 'one\rtwo\nthree\r\n'
+        result = i.append(None, None, None, teststr)
+        self.assertEqual(teststr, result)
+
     def test_that_Time2Internaldate_returns_a_result(self):
         # We can check only that it successfully produces a result,
         # not the correctness of the result itself, since the result