Fix empty ALLOW Response header for cls based View (#929)

We must check existing lower http method names for assembing
ALLOW header and passing into web.HTTPMethodNotAllowed.

aiohttp/web_urldispatcher.py

@@ -655,7 +655,8 @@ def __await__(self):
             return (yield from self.__iter__())
 
     def _raise_allowed_methods(self):
-        allowed_methods = {m for m in hdrs.METH_ALL if hasattr(self, m)}
+        allowed_methods = {
+            m for m in hdrs.METH_ALL if hasattr(self, m.lower())}
         raise HTTPMethodNotAllowed(self.request.method, allowed_methods)
 
 

tests/test_classbasedview.py

@@ -34,11 +34,13 @@ class MyView(View):
         @asyncio.coroutine
         def get(self):
             return web.Response(text='OK')
+        options = get
 
     request = mock.Mock()
     request.method = 'UNKNOWN'
     with pytest.raises(web.HTTPMethodNotAllowed) as ctx:
         yield from MyView(request)
+    assert ctx.value.headers['allow'] == 'GET,OPTIONS'
     assert ctx.value.status == 405
 
 
@@ -49,9 +51,11 @@ class MyView(View):
         @asyncio.coroutine
         def get(self):
             return web.Response(text='OK')
+        options = delete = get
 
     request = mock.Mock()
     request.method = 'POST'
     with pytest.raises(web.HTTPMethodNotAllowed) as ctx:
         yield from MyView(request)
+    assert ctx.value.headers['allow'] == 'DELETE,GET,OPTIONS'
     assert ctx.value.status == 405