Use a different port for test mode.

letsencrypt/plugins/standalone/authenticator.py

@@ -378,7 +378,10 @@ class StandaloneAuthenticator(common.Plugin):
                 results_if_failure.append(False)
         if not self.tasks:
             raise ValueError("nothing for .perform() to do")
-        if self.already_listening(challenges.DVSNI.PORT):
+        port = challenges.DVSNI.PORT
+        if self.config.test_mode:
+            port = 5001
+        if self.already_listening(port):
             # If we know a process is already listening on this port,
             # tell the user, and don't even attempt to bind it.  (This
             # test is Linux-specific and won't indicate that the port
@@ -386,7 +389,7 @@ class StandaloneAuthenticator(common.Plugin):
             return results_if_failure
         # Try to do the authentication; note that this creates
         # the listener subprocess via os.fork()
-        if self.start_listener(challenges.DVSNI.PORT, key):
+        if self.start_listener(port, key):
             return results_if_success
         else:
             # TODO: This should probably raise a DVAuthError exception