add test.

Author: devnexen

Lib/test/test_socket.py

@@ -1720,6 +1720,15 @@ def test_listen_backlog(self):
             srv.bind((HOST, 0))
             srv.listen()
 
+    def test_listen_backlog_connect(self):
+        for backlog in 0, -1:
+            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as srv:
+                srv.bind((HOST, 65200))
+                srv.listen(backlog)
+                with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as c:
+                    c.connect((HOST, 65200))
+                    c.send(MSG)
+
     @support.cpython_only
     def test_listen_backlog_overflow(self):
         # Issue 15989