diff --git a/devices/__init__.py b/devices/__init__.py
index bcd3698..46a2717 100644
--- a/devices/__init__.py
+++ b/devices/__init__.py
@@ -79,9 +79,15 @@ class group(object):
 
     def __getattribute__(self, name):
         def group_execution(*args, **kwargs):
+            rv_list = []
             for member in self[:]:
                 m = getattr(member, name)
-                m(*args, **kwargs)
+                rv_list.append(m(*args, **kwargs))
+            rv = rv_list[0]
+            for other in rv_list[1:]:
+                if other != rv:
+                    return None     # Hopefully None was not expected ;-)
+            return rv   # If all return values are identical
         try:
             rv = super().__getattribute__(name)
         except AttributeError:
diff --git a/smart_brain_test.py b/smart_brain_test.py
index ba62d88..7f9e5f8 100644
--- a/smart_brain_test.py
+++ b/smart_brain_test.py
@@ -6,7 +6,6 @@ from simulation.rooms import house
 import sys
 from tests.all import test_smarthome
 
-# TODO: Reimplement failed test(s)
 # TODO: Reimplement existing test
 # TODO: Extend tests in simulation
 #         - Test: Check of warning messages for battery and overtemperature
@@ -35,8 +34,13 @@ if __name__ == "__main__":
     h = house(mc, pd)
     for name in h.getmembers():
         d = h.getobjbyname(name)
-        for c in d.capabilities():
-            COMMANDS.append(name + '.' + c)
+        if d.capabilities() is None:
+            print("\n\n" + 2*"**********\n" + "\n" + name + "\n\n" + 2*"**********\n" + "\n\n")
+            print(type(d))
+            sys.exit(2)
+        else:
+            for c in d.capabilities():
+                COMMANDS.append(name + '.' + c)
     #
     ts = test_smarthome(h, mc)
     for name in ts.getmembers():