test: Always provide wsgi.error in environment during testWSGI.

caucase/test.py

@@ -1200,6 +1200,7 @@ class CaucaseTest(unittest.TestCase):
       """
       Non-standard shorthand for invoking the WSGI application.
       """
+      environ.setdefault('wsgi.errors', sys.stderr)
       start_response_list = []
       body = list(application(
         environ,
@@ -1263,7 +1264,6 @@ class CaucaseTest(unittest.TestCase):
       'PATH_INFO': '/cau/csr',
       'REQUEST_METHOD': 'PUT',
       'wsgi.input': StringIO(),
-      'wsgi.errors': StringIO(),
     })[0], 500)
     self.assertEqual(request({
       'PATH_INFO': '/cau/csr',