tests: use a random free port for smtp server (#44890)

tests/test_emails.py

@@ -5,6 +5,7 @@ import dns.resolver
 from dns import name
 from dns.rdtypes.ANY import MX, TXT
 import mock
+import random
 import smtplib
 import smtpd
 import socket
@@ -21,13 +22,24 @@ from test_manager import login
 
 
 @pytest.fixture
-def dns_resolver(monkeypatch):
+def port_available():
+    errno = 0
+    while not errno:
+        port = random.randint(49152, 65534)
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        errno = sock.connect_ex(('127.0.0.1', port))
+        sock.close()
+    return port
+
+
+@pytest.fixture
+def dns_resolver(monkeypatch, port_available):
     def fn(value, kind):
         if kind == 'MX':
             mx = mock.create_autospec(MX)
             mx.exchange = mock.create_autospec(name.Name)
             mx.exchange.to_text = mock.MagicMock()
-            mx.exchange.to_text.return_value = 'localhost:10025'
+            mx.exchange.to_text.return_value = 'localhost:%s' % port_available
             mx.preference = mock.create_autospec(name.Name)
             mx.preference.to_text = mock.MagicMock()
             mx.preference.to_text.return_value = 10
@@ -47,7 +59,7 @@ def dns_resolver(monkeypatch):
 
 
 @pytest.fixture
-def smtp_server(monkeypatch):
+def smtp_server(monkeypatch, port_available):
     class RecipientValidatingSMTPChannel(smtpd.SMTPChannel):
         def smtp_RCPT(self, arg):
             if six.PY2:
@@ -67,7 +79,7 @@ def smtp_server(monkeypatch):
             conn, addr = self.accept()
             channel = RecipientValidatingSMTPChannel(self, conn, addr)
 
-    server = MailServer(('localhost', 10025), None)
+    server = MailServer(('localhost', port_available), None)
     thread = threading.Thread(target=asyncore.loop, kwargs={'timeout': 1})
     thread.start()
     yield