tests: Add type narrowing for EmailMultiAlternatives.

Items in `django.core.mail.outbox` are by default typed as the less
general `EmailMessage` type. Before accessing the attribute
`alternatives`, we need to narrow the type to `EmailMultiAlternatives`.
Then narrow the tuple value we want to access to `str` before using
it in `assertIn` or `self.normalize_string`.

Signed-off-by: Zixuan James Li <p359101898@gmail.com>

zerver/tests/test_email_notifications.py

@@ -11,6 +11,7 @@ import lxml.html
 import orjson
 from django.conf import settings
 from django.core import mail
+from django.core.mail.message import EmailMultiAlternatives
 from django.test import override_settings
 from django.utils.timezone import now as timezone_now
 from django_auth_ldap.config import LDAPSearch
@@ -467,6 +468,7 @@ class TestMissedMessages(ZulipTestCase):
         else:
             reply_to_emails = ["noreply@testserver"]
         msg = mail.outbox[0]
+        assert isinstance(msg, EmailMultiAlternatives)
         from_email = str(Address(display_name="Zulip notifications", addr_spec=FromAddress.NOREPLY))
         self.assert_length(mail.outbox, 1)
         if send_as_user:
@@ -478,6 +480,7 @@ class TestMissedMessages(ZulipTestCase):
         self.assertIn(msg.reply_to[0], reply_to_emails)
         if verify_html_body:
             for text in verify_body_include:
+                assert isinstance(msg.alternatives[0][0], str)
                 self.assertIn(text, self.normalize_string(msg.alternatives[0][0]))
         else:
             for text in verify_body_include:
@@ -1132,12 +1135,16 @@ class TestMissedMessages(ZulipTestCase):
             ],
         )
 
+        assert isinstance(mail.outbox[0], EmailMultiAlternatives)
+        assert isinstance(mail.outbox[0].alternatives[0][0], str)
         self.assertIn("Iago: @**King Hamlet**\n\n--\nYou are", mail.outbox[0].body)
         # If message content starts with <p> tag the sender name is appended inside the <p> tag.
         self.assertIn(
             '<p><b>Iago</b>: <span class="user-mention"', mail.outbox[0].alternatives[0][0]
         )
 
+        assert isinstance(mail.outbox[1], EmailMultiAlternatives)
+        assert isinstance(mail.outbox[1].alternatives[0][0], str)
         self.assertIn("Iago: * 1\n *2\n\n--\nYou are receiving", mail.outbox[1].body)
         # If message content does not starts with <p> tag sender name is appended before the <p> tag
         self.assertIn(
@@ -1145,6 +1152,8 @@ class TestMissedMessages(ZulipTestCase):
             mail.outbox[1].alternatives[0][0],
         )
 
+        assert isinstance(mail.outbox[2], EmailMultiAlternatives)
+        assert isinstance(mail.outbox[2].alternatives[0][0], str)
         self.assertEqual("Hello\n\n--\n\nReply", mail.outbox[2].body[:16])
         # Sender name is not appended to message for PM missed messages
         self.assertIn(

zerver/tests/test_signup.py

@@ -11,6 +11,7 @@ from django.conf import settings
 from django.contrib.auth.views import PasswordResetConfirmView
 from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import ValidationError
+from django.core.mail.message import EmailMultiAlternatives
 from django.http import HttpRequest, HttpResponse
 from django.test import Client, override_settings
 from django.urls import reverse
@@ -1821,6 +1822,8 @@ earl-test@zulip.com""",
         self.check_sent_emails(["newuser@zulip.com"])
         from django.core.mail import outbox
 
+        assert isinstance(outbox[0], EmailMultiAlternatives)
+        assert isinstance(outbox[0].alternatives[0][0], str)
         body = self.normalize_string(outbox[0].alternatives[0][0])
 
         # Verify that one can't get Zulip to send invitation emails