Test fallback to legacy hello after connection is closed

Author: alcaeus

src/libmongoc/tests/test-mongoc-topology.c

@@ -2366,8 +2366,16 @@ _test_hello_ok (bool pooled)
          client, "admin", tmp_bson ("{'ping': 1}"), NULL, NULL, &error);
    }
 
+   /* Hang up to ensure that the next check runs legacy hello again */
    request = mock_server_receives_hello (server);
    BSON_ASSERT (request);
+   mock_server_hangs_up (request);
+   request_destroy (request);
+
+   /* The previous failure will trigger another handshake using legacy hello */
+   request = mock_server_receives_legacy_hello (
+      server, "{'" HANDSHAKE_CMD_LEGACY_HELLO "': 1, 'helloOk': true}");
+   BSON_ASSERT (request);
    mock_server_replies_simple (request, hello);
    request_destroy (request);