bpo-42756: Configure LMTP Unix-domain socket to use global default timeout when timeout not provided (GH-23969)

diff --git a/Lib/test/mock_socket.py b/Lib/test/mock_socket.py
index cda4db2..c7abddc 100644
--- a/Lib/test/mock_socket.py
+++ b/Lib/test/mock_socket.py
@@ -107,6 +107,9 @@ def getpeername(self):
     def close(self):
         pass
 
+    def connect(self, host):
+        pass
+
 
 def socket(family=None, type=None, proto=None):
     return MockSocket(family)
@@ -152,8 +155,12 @@ def getaddrinfo(*args, **kw):
 
 
 # Constants
+_GLOBAL_DEFAULT_TIMEOUT = socket_module._GLOBAL_DEFAULT_TIMEOUT
 AF_INET = socket_module.AF_INET
 AF_INET6 = socket_module.AF_INET6
 SOCK_STREAM = socket_module.SOCK_STREAM
 SOL_SOCKET = None
 SO_REUSEADDR = None
+
+if hasattr(socket_module, 'AF_UNIX'):
+    AF_UNIX = socket_module.AF_UNIX