add a decorator to add custom template filter

tests/flask_tests.py

@@ -311,6 +311,32 @@ class TemplatingTestCase(unittest.TestCase):
             macro = flask.get_template_attribute('_macro.html', 'hello')
             assert macro('World') == 'Hello World!'
 
+    def test_template_filter_not_called(self):
+        app = flask.Flask(__name__)
+        @app.template_filter
+        def my_reverse(s):
+            return s[::-1]
+        assert 'my_reverse' in  app.jinja_env.filters.keys()
+        assert app.jinja_env.filters['my_reverse'] == my_reverse
+        assert app.jinja_env.filters['my_reverse']('abcd') == 'dcba'
+
+    def test_template_filter_called(self):
+        app = flask.Flask(__name__)
+        @app.template_filter()
+        def my_reverse(s):
+            return s[::-1]
+        assert 'my_reverse' in  app.jinja_env.filters.keys()
+        assert app.jinja_env.filters['my_reverse'] == my_reverse
+        assert app.jinja_env.filters['my_reverse']('abcd') == 'dcba'
+
+    def test_template_filter_with_name(self):
+        app = flask.Flask(__name__)
+        @app.template_filter('strrev')
+        def my_reverse(s):
+            return s[::-1]
+        assert 'strrev' in  app.jinja_env.filters.keys()
+        assert app.jinja_env.filters['strrev'] == my_reverse
+        assert app.jinja_env.filters['strrev']('abcd') == 'dcba'
 
 def suite():
     from minitwit_tests import MiniTwitTestCase