diff --git a/Observer.py b/Observer.py
index dc40dd3..5ce4888 100644
--- a/Observer.py
+++ b/Observer.py
@@ -95,16 +95,9 @@ class Observable():
         if not isinstance(observer, Observer):
             raise TypeError("Unsubscriber must be Observer")
 
-        try:
-            if observer in self.obs_collection:
-                self.obs_collection.remove(observer)
-                #print "%s removed from collection" % (str(observer))
-            else:
-                pass
-                #print "%s not in collection" % (str(observer))
-
-        except TypeError:
-            print "Failed to remove %s" % (str(observer))
+        if not(observer in self.obs_collection):
+            raise ValueError("Observer not subscribed")
+        self.obs_collection.remove(observer)
 
     def __notify(self, mess):
         """
diff --git a/testObserver.py b/testObserver.py
index b65359e..78573d4 100644
--- a/testObserver.py
+++ b/testObserver.py
@@ -86,14 +86,17 @@ class TestObserver(unittest.TestCase):
         self.assertEquals(len(self.myObservable.obs_collection), 2)
 
     def testUnsubscribe(self):
-        pass
+        self.myObservable.subscribe(self.myObserver1)
+        self.myObservable.subscribe(self.myObserver2)
+        self.assertEquals(len(self.myObservable.obs_collection), 2)
+        self.myObservable.unsubscribe(self.myObserver1)
+        self.assertEquals(len(self.myObservable.obs_collection), 1)
+
+        self.assertRaises(ValueError, lambda: self.myObservable.unsubscribe(self.myObserver1))  # already removed
+        self.assertRaises(TypeError, lambda: self.myObservable.unsubscribe("Georges"))
 
     def testNotify(self):
         pass
 
-    def testNameUnicity(self):
-        pass
-
-
 if __name__ == '__main__':
     unittest.main()
\ No newline at end of file