Test example update (#236)

* Test example update

because of @with_injector gone according to https://github.com/python-injector/injector/issues/146

Reported also on https://github.com/python-injector/injector/issues/220

* Cleanup

docs/testing.rst

@@ -1,24 +1,23 @@
 Testing with Injector
 =====================
 
-When you use unit test framework such as `unittest2` or `nose` you can also profit from `injector`. However, manually creating injectors and test classes can be quite annoying. There is, however, `with_injector` method decorator which has parameters just as `Injector` construtor and installes configured injector into class instance on the time of method call::
+When you use unit test framework such as `unittest2` or `nose` you can also profit from `injector`. ::
 
     import unittest
-    from injector import Module, with_injector, inject
+    from injector import Injector, Module
+
 
     class UsernameModule(Module):
         def configure(self, binder):
             binder.bind(str, 'Maria')
 
-    class TestSomethingClass(unittest.TestCase):
-        @with_injector(UsernameModule())
-        def setUp(self):
-            pass
 
-        @inject
+    class TestSomethingClass(unittest.TestCase):
-        def test_username(self, username: str):
+
+        def setUp(self):
+            self.__injector = Injector(UsernameModule())
+
+        def test_username(self):
+            username = self.__injector.get(str)
             self.assertEqual(username, 'Maria')
 
-**Each** method call re-initializes :class:`~injector.Injector` - if you want to you can also put :func:`~injector.with_injector` decorator on class constructor.
-
-After such call all :func:`~injector.inject`-decorated methods will work just as you'd expect them to work.