tests: use strings in email mocking (#36515)

tests/utilities.py

@@ -14,8 +14,10 @@ from wcs import sql, sessions
 from webtest import TestApp
 from quixote import cleanup, get_publisher
 from django.conf import settings
+from django.utils.encoding import force_text
 from django.utils.six.moves.urllib import parse as urlparse
 
+from wcs.qommon import force_str
 import wcs
 import wcs.wsgi
 from wcs import publisher, compat
@@ -237,14 +239,14 @@ class EmailsMocking(object):
                 else:
                     payload = msg.get_payload(decode=True)
                     payloads = [payload]
-                self.emails[subject] = {
+                self.emails[force_text(subject)] = {
                         'from': msg_from,
                         'to': email.header.decode_header(msg['To'])[0][0],
-                        'payload': payload,
+                        'payload': force_str(payload if payload else ''),
                         'payloads': payloads,
                         'msg': msg,
                         }
-                self.emails[subject]['email_rcpt'] = rcpts
+                self.emails[force_text(subject)]['email_rcpt'] = rcpts
 
             def close(self):
                 pass