Issue #15989: Fix several occurrences of integer overflow
when result of PyLong_AsLong() narrowed to int without checks.

This is a backport of changesets 13e2e44db99d and 525407d89277.
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index e40b21e..5573421 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -7,6 +7,7 @@
 import io
 import socket
 import select
+import _testcapi
 import time
 import traceback
 import queue
@@ -850,11 +851,17 @@
             self.assertRaises(ValueError, fp.writable)
             self.assertRaises(ValueError, fp.seekable)
 
-    def testListenBacklog0(self):
+    def test_listen_backlog(self):
+        for backlog in 0, -1:
+            srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+            srv.bind((HOST, 0))
+            srv.listen(backlog)
+            srv.close()
+
+        # Issue 15989
         srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         srv.bind((HOST, 0))
-        # backlog = 0
-        srv.listen(0)
+        self.assertRaises(OverflowError, srv.listen, _testcapi.INT_MAX + 1)
         srv.close()
 
     @unittest.skipUnless(SUPPORTS_IPV6, 'IPv6 required for this test.')
@@ -954,6 +961,11 @@
 
     def _testShutdown(self):
         self.serv_conn.send(MSG)
+        # Issue 15989
+        self.assertRaises(OverflowError, self.serv_conn.shutdown,
+                          _testcapi.INT_MAX + 1)
+        self.assertRaises(OverflowError, self.serv_conn.shutdown,
+                          2 + (_testcapi.UINT_MAX + 1))
         self.serv_conn.shutdown(2)
 
     def testDetach(self):
@@ -1067,7 +1079,10 @@
 
     def testSetBlocking(self):
         # Testing whether set blocking works
-        self.serv.setblocking(0)
+        self.serv.setblocking(True)
+        self.assertIsNone(self.serv.gettimeout())
+        self.serv.setblocking(False)
+        self.assertEqual(self.serv.gettimeout(), 0.0)
         start = time.time()
         try:
             self.serv.accept()
@@ -1075,6 +1090,10 @@
             pass
         end = time.time()
         self.assertTrue((end - start) < 1.0, "Error setting non-blocking mode.")
+        # Issue 15989
+        if _testcapi.UINT_MAX < _testcapi.ULONG_MAX:
+            self.serv.setblocking(_testcapi.UINT_MAX + 1)
+            self.assertIsNone(self.serv.gettimeout())
 
     def _testSetBlocking(self):
         pass