bpo-395222: Correctly unparse unicode prefix in ast_unparse.c (GH-19512)

diff --git a/Lib/test/test_future.py b/Lib/test/test_future.py
index ebeb833..0522003 100644
--- a/Lib/test/test_future.py
+++ b/Lib/test/test_future.py
@@ -153,6 +153,7 @@
         eq = self.assertAnnotationEqual
         eq('...')
         eq("'some_string'")
+        eq("u'some_string'")
         eq("b'\\xa3'")
         eq('Name')
         eq('None')