bpo-39793: use the same domain on make_msgid tests (GH-18698) (GH-19554)

(cherry picked from commit 5565c30f0b25996a0e73477fc0e1e1aced52b926)

Co-authored-by: Batuhan Taşkaya <batuhanosmantaskaya@gmail.com>
diff --git a/Lib/test/test_email/test_email.py b/Lib/test/test_email/test_email.py
index 5414cf0..9e5c6ad 100644
--- a/Lib/test/test_email/test_email.py
+++ b/Lib/test/test_email/test_email.py
@@ -11,8 +11,8 @@
 from io import StringIO, BytesIO
 from itertools import chain
 from random import choice
-from socket import getfqdn
 from threading import Thread
+from unittest.mock import patch
 
 import email
 import email.policy
@@ -3342,9 +3342,11 @@
             '.test-idstring@testdomain-string>')
 
     def test_make_msgid_default_domain(self):
-        self.assertTrue(
-            email.utils.make_msgid().endswith(
-                '@' + getfqdn() + '>'))
+        with patch('socket.getfqdn') as mock_getfqdn:
+            mock_getfqdn.return_value = domain = 'pythontest.example.com'
+            self.assertTrue(
+                email.utils.make_msgid().endswith(
+                    '@' + domain + '>'))
 
     def test_Generator_linend(self):
         # Issue 14645.
diff --git a/Misc/NEWS.d/next/Tests/2020-02-29-12-58-17.bpo-39793.Og2SUN.rst b/Misc/NEWS.d/next/Tests/2020-02-29-12-58-17.bpo-39793.Og2SUN.rst
new file mode 100644
index 0000000..6fa0d15
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2020-02-29-12-58-17.bpo-39793.Og2SUN.rst
@@ -0,0 +1 @@
+Use the same domain when testing ``make_msgid``. Patch by Batuhan Taskaya.