Currently (135c6a56e55d2f4f8718b3b9f03ce3c692b15f0f) the following test fails:

./python -m test.regrtest -v test_tools.test_unparse -u cpu

(Note that -u cpu is needed to force test_unparse.DirectoryTestCase to check all files under Lib/ and Lib/test/.)

An example error message:

======================================================================
FAIL: test_files (test.test_tools.test_unparse.DirectoryTestCase) (filename='/home/yen/Projects/cpython/Lib/test/test_typing.py'
)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/yen/Projects/cpython/Lib/test/test_tools/test_unparse.py", line 309, in test_files
    self.check_roundtrip(source)
  File "/home/yen/Projects/cpython/Lib/test/test_tools/test_unparse.py", line 132, in check_roundtrip
    self.assertASTEqual(ast1, ast2)
  File "/home/yen/Projects/cpython/Lib/test/test_tools/test_unparse.py", line 124, in assertASTEqual
    self.assertEqual(ast.dump(ast1), ast.dump(ast2))
AssertionError: 'Modu[88178 chars]kind=\'u\')], ctx=Load())), ctx=Load()))], dec[421987 chars]=[])' != 'Modu[88178 chars]kind=No
ne)], ctx=Load())), ctx=Load()))], deco[421986 chars]=[])'

----------------------------------------------------------------------

Apparently that's because Tools/parser/unparse.py does not handle strings like u"bar" correctly. I managed to "fix" it with the following patch:

diff --git a/Tools/parser/unparse.py b/Tools/parser/unparse.py
index 385902ef4b..a25b5e49df 100644
--- a/Tools/parser/unparse.py
+++ b/Tools/parser/unparse.py
@@ -399,6 +399,8 @@ class Unparser:
         elif value is ...:
             self.write("...")
         else:
+            if t.kind == 'u':
+                self.write("u")
             self._write_constant(t.value)

     def _List(self, t):

Not sure if this is the correct approach, though.