Add tests for processing emailed-in stream messages (success & fail)

Prior to adding reply-to-missed-message-email functionality, adding
automated tests for simpler case - incoming stream messages. Added
to new file test_email_mirror.py.
Also removed the "if not body" code from process_stream_message that
will never run because of an upstream ZulipEmailForwardError exception.

zerver/lib/email_mirror.py

@@ -255,10 +255,6 @@ def process_stream_message(to, subject, message, debug_info):
     body = filter_footer(extract_body(message))
     body += extract_and_upload_attachments(message, stream.realm)
     debug_info["stream"] = stream
-    if not body:
-        # You can't send empty Zulips, so to avoid confusion over the
-        # email forwarding failing, set a dummy message body.
-        body = "(No email body)"
     send_zulip(stream, subject, body)
 
 def process_missed_message(to, message, pre_checked):

zerver/test_email_mirror.py

@@ -0,0 +1,94 @@
+# -*- coding: utf-8 -*-
+from __future__ import absolute_import
+
+from django.test import TestCase
+
+from zerver.lib.test_helpers import (
+    AuthedTestCase,
+    most_recent_message,
+)
+
+from zerver.models import (
+    get_display_recipient, get_stream, get_user_profile_by_email,
+)
+
+from zerver.lib.actions import (
+    encode_email_address, do_update_message_flags,
+)
+from zerver.lib.email_mirror import (
+    process_message, process_stream_message, ZulipEmailForwardError,
+)
+from email.mime.text import MIMEText
+
+import datetime
+import time
+import re
+import ujson
+
+
+class TestStreamEmailMessagesSuccess(AuthedTestCase):
+    def test_receive_stream_email_messages_success(self):
+
+        # build dummy messages for stream
+        # test valid incoming stream message is processed properly
+        self.login("hamlet@zulip.com")
+        user_profile = get_user_profile_by_email("hamlet@zulip.com")
+        self.subscribe_to_stream(user_profile.email, "Denmark")
+        stream = get_stream("Denmark", user_profile.realm)
+
+        stream_to_address = encode_email_address(stream)
+        headers = {}
+        headers['Reply-To'] = 'othello@zulip.com'
+
+        incoming_valid_message = MIMEText('TestStreamEmailMessages Body')
+
+        incoming_valid_message['Subject'] = 'TestStreamEmailMessages Subject'
+        incoming_valid_message['From'] = "hamlet@zulip.com"
+        incoming_valid_message['To'] = stream_to_address
+        incoming_valid_message['Reply-to'] = "othello@zulip.com"
+
+        process_message(incoming_valid_message)
+
+        # Hamlet is subscribed to this stream so should see the email message from Othello.
+        message = most_recent_message(user_profile)
+
+        self.assertEqual(message.content, "TestStreamEmailMessages Body")
+        self.assertEqual(get_display_recipient(message.recipient), stream.name)
+        self.assertEqual(message.subject, incoming_valid_message['Subject'])
+
+class TestStreamEmailMessagesEmptyBody(AuthedTestCase):
+    def test_receive_stream_email_messages_empty_body(self):
+
+        # build dummy messages for stream
+        # test message with empty body is not sent
+        self.login("hamlet@zulip.com")
+        user_profile = get_user_profile_by_email("hamlet@zulip.com")
+        self.subscribe_to_stream(user_profile.email, "Denmark")
+        stream = get_stream("Denmark", user_profile.realm)
+
+        stream_to_address = encode_email_address(stream)
+        headers = {}
+        headers['Reply-To'] = 'othello@zulip.com'
+
+        # empty body
+        incoming_valid_message = MIMEText('')
+
+        incoming_valid_message['Subject'] = 'TestStreamEmailMessages Subject'
+        incoming_valid_message['From'] = "hamlet@zulip.com"
+        incoming_valid_message['To'] = stream_to_address
+        incoming_valid_message['Reply-to'] = "othello@zulip.com"
+
+        exception_message = ""
+        debug_info = {}
+
+        # process_message eats the exception & logs an error which can't be parsed here
+        # so calling process_stream_message directly
+        try:
+            process_stream_message(incoming_valid_message['To'],
+                incoming_valid_message['Subject'],
+                incoming_valid_message,
+                debug_info)
+        except ZulipEmailForwardError, e:
+            # empty body throws exception
+            exception_message = e.message
+        self.assertEqual(exception_message, "Unable to find plaintext or HTML message body")