Pass through test_mode with another request method

Hello,
In one of my rails app, I use Omniauth with multiple providers.
For each one, I can disconnect by calling a DELETE on `auth/:provider`

````
GET|POST /auth/:provider(.:format)            identities#passthru
GET|POST /auth/:provider/callback(.:format)   identities#callback 
DELETE   /auth/:provider(.:format)            identities#destroy
````

It works fine except on `test_mode`, where destroy requests are mapped as request phases.