can add new config with mixconfig type

tests/test_mixconfig.py

@@ -6,7 +6,7 @@ from py.test import raises
 from tiramisu.setting import groups, owners
 from tiramisu import IntOption, StrOption, NetworkOption, NetmaskOption, \
                      OptionDescription, Leadership, Config, GroupConfig, MixConfig, \
-                     Params, ParamOption, ParamValue
+                     MetaConfig, Params, ParamOption, ParamValue
 from tiramisu.error import ConfigError, ConflictError, PropertiesOptionError, LeadershipError, APIError
 from tiramisu.storage import list_sessions
 
@@ -1122,3 +1122,10 @@ def test_mix_add_config_readd():
     config = Config(od, session_id='new')
     mix.config.add(config)
     raises(ConflictError, "mix2.config.add(config)")
+
+
+def test_meta_new_mixconfig():
+    od = make_description()
+    conf = Config(od, session_id='conf1')
+    meta = MetaConfig([conf])
+    assert isinstance(meta.config.new('mixconfig', type="mixconfig"), MixConfig)