diff --git a/aircox/controllers/diffusions.py b/aircox/controllers/diffusions.py
deleted file mode 100644
index 2527ecb..0000000
--- a/aircox/controllers/diffusions.py
+++ /dev/null
@@ -1,58 +0,0 @@
-import datetime
-import logging
-
-from django.db import transaction
-
-from aircox.models import Diffusion, Schedule
-
-logger = logging.getLogger("aircox.commands")
-
-
-__all__ = ("Diffusions",)
-
-
-class Diffusions:
-    """Handle generation and update of Diffusion instances."""
-
-    date = None
-
-    def __init__(self, date):
-        self.date = date or datetime.date.today()
-
-    def update(self):
-        episodes, diffusions = [], []
-        for schedule in Schedule.objects.filter(
-            program__active=True, initial__isnull=True
-        ):
-            eps, diffs = schedule.diffusions_of_month(self.date)
-            if eps:
-                episodes += eps
-            if diffs:
-                diffusions += diffs
-
-            logger.info(
-                "[update] %s: %d episodes, %d diffusions and reruns",
-                str(schedule),
-                len(eps),
-                len(diffs),
-            )
-
-        with transaction.atomic():
-            logger.info(
-                "[update] save %d episodes and %d diffusions",
-                len(episodes),
-                len(diffusions),
-            )
-            for episode in episodes:
-                episode.save()
-            for diffusion in diffusions:
-                # force episode id's update
-                diffusion.episode = diffusion.episode
-                diffusion.save()
-
-    def clean(self):
-        qs = Diffusion.objects.filter(
-            type=Diffusion.TYPE_UNCONFIRMED, start__lt=self.date
-        )
-        logger.info("[clean] %d diffusions will be removed", qs.count())
-        qs.delete()
diff --git a/aircox/test.py b/aircox/test.py
index c67f2f3..d5c61b0 100644
--- a/aircox/test.py
+++ b/aircox/test.py
@@ -86,7 +86,7 @@ class WrapperMixin:
         ns_target = getattr(ns, ns_attr, None)
         if self.target is ns_target:
             return
-        elif self.target is not None:
+        elif self.target is not None and self.ns:
             raise RuntimeError(
                 "self target already injected. It must be "
                 "`release` before `inject`."
@@ -97,12 +97,14 @@ class WrapperMixin:
 
         self.ns = ns
         self.ns_attr = ns_attr
+        return self
 
     def release(self):
         """Remove injection from previously injected parent, reset target."""
         if self.ns_target is self.interface:
             setattr(self.ns, self.ns_attr, self.target)
         self.target = None
+        return self
 
 
 class SpoofMixin:
@@ -190,6 +192,16 @@ class Interface:
             self.interface = interface
             super().__init__(**kwargs)
 
+        def clone(self, **kwargs):
+            """Return an Interface copying some values from self."""
+            kwargs.update(
+                {
+                    "target": self.target,
+                    "funcs": self.funcs,
+                }
+            )
+            return type(self.interface)(_imeta_kw=kwargs)._imeta
+
         def __getitem__(self, name):
             return self.traces[name]
 
diff --git a/aircox/tests/conftest.py b/aircox/tests/conftest.py
index 7e6833b..37342cf 100644
--- a/aircox/tests/conftest.py
+++ b/aircox/tests/conftest.py
@@ -1,10 +1,20 @@
 from datetime import time, timedelta
 import itertools
+import logging
 
 import pytest
 from model_bakery import baker
 
 from aircox import models
+from aircox.test import Interface
+
+
+@pytest.fixture
+def logger():
+    logger = Interface(
+        logging, {"info": None, "debug": None, "error": None, "warning": None}
+    )
+    return logger
 
 
 @pytest.fixture
diff --git a/aircox/tests/controllers/test_diffusions.py b/aircox/tests/controllers/test_diffusions.py
deleted file mode 100644
index dc4a153..0000000
--- a/aircox/tests/controllers/test_diffusions.py
+++ /dev/null
@@ -1,19 +0,0 @@
-import pytest
-
-from aircox.controllers.diffusions import Diffusions
-
-
-@pytest.fixture
-def diffusions():
-    return Diffusions
-
-
-class TestDiffusion:
-    def test___init__(self):
-        pass
-
-    def test_update(self):
-        pass
-
-    def test_clean(self):
-        pass
diff --git a/aircox/tests/controllers/test_sound_monitor.py b/aircox/tests/controllers/test_sound_monitor.py
index b792346..e163fec 100644
--- a/aircox/tests/controllers/test_sound_monitor.py
+++ b/aircox/tests/controllers/test_sound_monitor.py
@@ -1,5 +1,4 @@
 from concurrent import futures
-import logging
 import pytest
 
 from django.utils import timezone as tz
@@ -18,14 +17,6 @@ def event():
     return Interface(src_path="/tmp/src_path", dest_path="/tmp/dest_path")
 
 
-@pytest.fixture
-def logger():
-    logger = Interface(
-        logging, {"info": None, "debug": None, "error": None, "warning": None}
-    )
-    return logger
-
-
 @pytest.fixture
 def interfaces():
     items = {
diff --git a/aircox_streamer/tests/conftest.py b/aircox_streamer/tests/conftest.py
index 2778272..782c1b0 100644
--- a/aircox_streamer/tests/conftest.py
+++ b/aircox_streamer/tests/conftest.py
@@ -18,36 +18,6 @@ local_tz = tzlocal.get_localzone()
 working_dir = os.path.join(os.path.dirname(__file__), "working_dir")
 
 
-def interface_wrap(obj, attr, value):
-    if not isinstance(getattr(obj, "calls", None), dict):
-        obj.calls = {}
-    obj.calls[attr] = None
-
-    def wrapper(*a, **kw):
-        call = obj.calls.get(attr)
-        if call is None:
-            obj.calls[attr] = (a, kw)
-        elif isinstance(call, tuple):
-            obj.calls[attr] = [call, (a, kw)]
-        else:
-            call.append((a, kw))
-        return value
-
-    setattr(obj, attr, wrapper)
-
-
-def interface(obj, funcs):
-    """Override provided object's functions using dict of funcs, as ``{
-    func_name: return_value}``.
-
-    Attribute ``obj.calls`` is a dict
-    with all call done using those methods, as
-    ``{func_name: (args, kwargs)}``.
-    """
-    for attr, value in funcs.items():
-        interface_wrap(obj, attr, value)
-
-
 class FakeSocket:
     FAILING_ADDRESS = -1
     """Connect with this address fails."""