Raise assertion errors if @api_view decorator is applied incorrectly. Fixes #596.

rest_framework/decorators.py

 from rest_framework.views import APIView
+import types
 
 
 def api_view(http_method_names):
@@ -23,6 +24,14 @@ def api_view(http_method_names):
         #         pass
         #     WrappedAPIView.__doc__ = func.doc    <--- Not possible to do this
 
+        # api_view applied without (method_names)
+        assert not(isinstance(http_method_names, types.FunctionType)), \
+            '@api_view missing list of allowed HTTP methods'
+
+        # api_view applied with eg. string instead of list of strings
+        assert isinstance(http_method_names, (list, tuple)), \
+            '@api_view expected a list of strings, recieved %s' % type(http_method_names).__name__
+
         allowed_methods = set(http_method_names) | set(('options',))
         WrappedAPIView.http_method_names = [method.lower() for method in allowed_methods]
 

rest_framework/tests/decorators.py

@@ -28,6 +28,28 @@ class DecoratorTestCase(TestCase):
         response.request = request
         return APIView.finalize_response(self, request, response, *args, **kwargs)
 
+    def test_api_view_incorrect(self):
+        """
+        If @api_view is not applied correct, we should raise an assertion.
+        """
+
+        @api_view
+        def view(request):
+            return Response()
+
+        request = self.factory.get('/')
+        self.assertRaises(AssertionError, view, request)
+
+    def test_api_view_incorrect_arguments(self):
+        """
+        If @api_view is missing arguments, we should raise an assertion.
+        """
+
+        with self.assertRaises(AssertionError):
+            @api_view('GET')
+            def view(request):
+                return Response()
+
     def test_calling_method(self):
 
         @api_view(['GET'])