PYTHON-1897 Don't open new threads/sockets when closing a client

pymongo/topology.py

@@ -431,7 +431,9 @@ class Topology(object):
 
             # Mark all servers Unknown.
             self._description = self._description.reset()
-            self._update_servers()
+            for address, sd in self._description.server_descriptions().items():
+                if address in self._servers:
+                    self._servers[address].description = sd
 
             # Stop SRV polling thread.
             if self._srv_monitor:

test/test_client.py

@@ -743,6 +743,13 @@ class TestClient(IntegrationTest):
         client.close()
         self.assertTrue(client._kill_cursors_executor._stopped)
 
+    def test_close_does_not_open_servers(self):
+        client = rs_client(connect=False)
+        topology = client._topology
+        self.assertEqual(topology._servers, {})
+        client.close()
+        self.assertEqual(topology._servers, {})
+
     def test_bad_uri(self):
         with self.assertRaises(InvalidURI):
             MongoClient("http://localhost")