PYTHON-2935 Fix test_encryption.TestClientSimple.test_use_after_close (#751)

Author: ShaneHarvey

pymongo/topology.py

@@ -556,10 +556,8 @@ def _ensure_opened(self):
         Hold the lock when calling this.
         """
         if self._closed:
-            raise InvalidOperation("Once a MongoClient is closed, "
-                                   "all operations will fail. Please create "
-                                   "a new client object if you wish to "
-                                   "reconnect.")
+            raise InvalidOperation("Cannot use MongoClient after close")
+
         if not self._opened:
             self._opened = True
             self._update_servers()