diff --git a/test/test_cache.py b/test/test_cache.py
index 13d44e3..32704e8 100644
--- a/test/test_cache.py
+++ b/test/test_cache.py
@@ -12,13 +12,20 @@ from tiramisu.option import BoolOption, IPOption, IntOption, StrOption, OptionDe
 from tiramisu import Config
 from tiramisu.error import ConfigError, PropertiesOptionError
 from tiramisu.setting import groups
-from tiramisu import undefined, Params, ParamValue, ParamOption
+from tiramisu import undefined, Params, ParamValue, ParamOption, \
+                     list_sessions, default_storage, delete_session
 from tiramisu.api import TIRAMISU_VERSION
-from tiramisu.storage import list_sessions
 
 
 def teardown_function(function):
-    assert list_sessions() == [], 'session list is not empty when leaving "{}"'.format(function.__name__)
+    if default_storage.is_persistent:
+        sessions = list_sessions()
+        if not sessions:
+            return
+        assert len(sessions) == 1
+        delete_session(sessions[0])
+    else:
+        assert list_sessions() == [], 'session list is not empty when leaving "{}"'.format(function.__name__)
 
 
 global incr
diff --git a/test/test_choice_option.py b/test/test_choice_option.py
index 3bf51ed..b521eb6 100644
--- a/test/test_choice_option.py
+++ b/test/test_choice_option.py
@@ -5,8 +5,7 @@ from .autopath import do_autopath
 do_autopath()
 
 from tiramisu.setting import owners
-from tiramisu.option import ChoiceOption, StrOption, OptionDescription
-from tiramisu import Config
+from tiramisu import ChoiceOption, StrOption, OptionDescription, Config
 from tiramisu.error import ConfigError
 from tiramisu import undefined, Params, ParamValue, ParamOption
 from tiramisu.api import TIRAMISU_VERSION
diff --git a/tiramisu/__init__.py b/tiramisu/__init__.py
index e2ff65b..4826832 100644
--- a/tiramisu/__init__.py
+++ b/tiramisu/__init__.py
@@ -19,7 +19,7 @@ from .error import APIError
 from .api import Config, MetaConfig, GroupConfig, MixConfig
 from .option import __all__ as all_options
 from .setting import owners, undefined
-from .storage import default_storage_type, StorageType, list_sessions, \
+from .storage import default_storage, Storage, list_sessions, \
                      delete_session
 
 
@@ -33,8 +33,8 @@ allfuncs = ['Params',
             'Config',
             'APIError',
             'undefined',
-            'default_storage_type',
-            'StorageType',
+            'default_storage',
+            'Storage',
             'list_sessions',
             'delete_session',
             'tiramisu_copy']
diff --git a/tiramisu/storage/__init__.py b/tiramisu/storage/__init__.py
index 234f379..5d52679 100644
--- a/tiramisu/storage/__init__.py
+++ b/tiramisu/storage/__init__.py
@@ -26,38 +26,31 @@ Storage is basic components used to set Config informations in DB.
 
 from time import time
 from random import randint
-import os
+from os import environ
+from os.path import split
+from typing import Dict
 from ..error import ConfigError
 from ..i18n import _
 
 
-MODULE_PATH = os.path.split(os.path.split(os.path.split(__file__)[0])[0])[1]
+DEFAULT_STORAGE = MEMORY_STORAGE = 'dictionary'
+MODULE_PATH = split(split(split(__file__)[0])[0])[1]
 
 
-MEMORY_STORAGE = 'dictionary'
-DEFAULT_STORAGE = MEMORY_STORAGE
-
-
-class StorageType(object):
+class Storage:
     """Object to store storage's type. If a Config is already set,
     default storage is store as selected storage. You cannot change it
     after.
     """
-    default_storage = os.environ.get('TIRAMISU_STORAGE', DEFAULT_STORAGE)
-    storage_type = None
-    mod = None
-
-    def set(self, name):
-        if self.storage_type is not None:  # pragma: no cover
-            if self.storage_type == name:
-                return
-            raise ConfigError(_('storage_type is already set, '
-                                'cannot rebind it'))
-        self.storage_type = name
+    def __init__(self,
+                 **kwargs: Dict[str, str]) -> None:
+        self.storage_type = None
+        self.mod = None
+        self.setting(**kwargs)
 
     def get(self):
         if self.storage_type is None:
-            self.storage_type = self.default_storage
+            self.storage_type = environ.get('TIRAMISU_STORAGE', DEFAULT_STORAGE)
         if self.mod is None:
             modulepath = '{0}.storage.{1}'.format(MODULE_PATH,
                                                   self.storage_type)
@@ -65,21 +58,33 @@ class StorageType(object):
                 mod = __import__(modulepath)
             except ImportError:  # pragma: no cover
                 raise SystemError(_('cannot import the storage {0}').format(
-                    self.default_storage))
+                    self.storage_type))
             for token in modulepath.split(".")[1:]:
                 mod = getattr(mod, token)
             self.mod = mod
         return self.mod
 
-    def setting(self, **kwargs):
+    def setting(self,
+                **kwargs: Dict[str, str]) -> None:
+        if 'engine' in kwargs:
+            name = kwargs['engine']
+            if self.storage_type is not None and self.storage_type != name:  # pragma: no cover
+                raise ConfigError(_('storage_type is already set, '
+                                    'cannot rebind it'))
+            self.storage_type = name
+            del kwargs['engine']
+        if kwargs:
+            mod = self.get()
+            for key, value in kwargs.items():
+                setattr(mod.SETTING, key, value)
+
+    def is_persistent(self):
         mod = self.get()
-        for key, value in kwargs.items():
-            setattr(mod.SETTING, key, value)
+        return mod.PERSISTENT
 
 
-default_storage_type = StorageType()
-memory_storage = StorageType()
-memory_storage.set(MEMORY_STORAGE)
+default_storage = Storage()
+memory_storage = Storage(engine=MEMORY_STORAGE)
 
 
 def gen_storage_id(session_id,
@@ -96,7 +101,7 @@ def get_storages(context,
     session_id = gen_storage_id(session_id,
                                 context)
     if storage is None:
-        storage = default_storage_type
+        storage = default_storage
     imp = storage.get()
     imp_storage = imp.Storage(session_id,
                               persistent)
@@ -120,18 +125,18 @@ def get_default_settings_storages():
     return properties, permissives
 
 
-def list_sessions():
+def list_sessions(storage=default_storage):
     """List all available session (persistent or not persistent)
     """
-    return default_storage_type.get().list_sessions()
+    return storage.get().list_sessions()
 
 
-def delete_session(session_id):
+def delete_session(session_id, storage=default_storage):
     """Delete a selected session, be careful, you can deleted a session
     use by an other instance
     :params session_id: id of session to delete
     """
-    storage_module = default_storage_type.get()
+    storage_module = storage.get()
     session = storage_module.storage.getsession()
     storage_module.value.delete_session(session_id)
     storage_module.storage.delete_session(session_id)
diff --git a/tiramisu/storage/dictionary/__init__.py b/tiramisu/storage/dictionary/__init__.py
index 43d53e5..3373235 100644
--- a/tiramisu/storage/dictionary/__init__.py
+++ b/tiramisu/storage/dictionary/__init__.py
@@ -24,10 +24,11 @@ use it. But if something goes wrong, you will lost your modifications.
 """
 from .value import Values
 from .setting import Properties, Permissives
-from .storage import SETTING, Storage, list_sessions
+from .storage import PERSISTENT, SETTING, Storage, list_sessions
 
 
-__all__ = ('SETTING',
+__all__ = ('PERSISTENT',
+           'SETTING',
            'Values',
            'Properties',
            'Permissives',
diff --git a/tiramisu/storage/dictionary/setting.py b/tiramisu/storage/dictionary/setting.py
index 6bd9642..8dc5ef3 100644
--- a/tiramisu/storage/dictionary/setting.py
+++ b/tiramisu/storage/dictionary/setting.py
@@ -57,8 +57,8 @@ class Properties(Cache):
         return copy(self._properties)
 
     def importation(self, properties):
-        self.reset_all_cache()
         self._properties = properties
+        self.reset_all_cache()
 
 
 class Permissives(Cache):
diff --git a/tiramisu/storage/dictionary/storage.py b/tiramisu/storage/dictionary/storage.py
index b97c4e6..f4fffac 100644
--- a/tiramisu/storage/dictionary/storage.py
+++ b/tiramisu/storage/dictionary/storage.py
@@ -26,6 +26,7 @@ class Setting:
 
 SETTING = Setting()
 _list_sessions = []
+PERSISTENT = False
 
 
 def list_sessions():
diff --git a/tiramisu/storage/sqlite3/__init__.py b/tiramisu/storage/sqlite3/__init__.py
index 2b02520..10cad94 100644
--- a/tiramisu/storage/sqlite3/__init__.py
+++ b/tiramisu/storage/sqlite3/__init__.py
@@ -22,10 +22,11 @@ You should not configure differents Configs with same session_id.
 """
 from .value import Values
 from .setting import Properties, Permissives
-from .storage import SETTING, Storage, list_sessions
+from .storage import PERSISTENT, SETTING, Storage, list_sessions
 
 
-__all__ = ('SETTING',
+__all__ = ('PERSISTENT',
+           'SETTING',
            'Values',
            'Properties',
            'Permissives',
diff --git a/tiramisu/storage/sqlite3/setting.py b/tiramisu/storage/sqlite3/setting.py
index 24bc5f9..f7adaba 100644
--- a/tiramisu/storage/sqlite3/setting.py
+++ b/tiramisu/storage/sqlite3/setting.py
@@ -76,6 +76,7 @@ class Properties(Sqlite3DB):
                                                        self._session_id,
                                                       ), False)
         self._storage._conn.commit()
+        self.reset_all_cache()
 
 
 class Permissives(Sqlite3DB):
diff --git a/tiramisu/storage/sqlite3/storage.py b/tiramisu/storage/sqlite3/storage.py
index 897de6d..81b17fc 100644
--- a/tiramisu/storage/sqlite3/storage.py
+++ b/tiramisu/storage/sqlite3/storage.py
@@ -46,6 +46,7 @@ class Setting:
         super().__setattr__(key, value)
 
 
+PERSISTENT = True
 SETTING = Setting()