RSpec testing Devise SessionController with Jbuilder view

I'm using RSpec for testing a SessionsController I am overriding from Devise in my Rails application:
class Users::SessionsController < Devise::SessionsController

The sign_in method renders a jbuilder view:
render '/users/sign_in', status: :ok

I get the expected result when testing the view using curl. But I haven't been able to make this work with my specs. I get the following error:

 Failure/Error: post '/users/sign_in', @data, format: 'json' ActionView::MissingTemplate: Missing template users/sign_in with {:locale=>[:en], :formats=>[:html], :variants=>[], :handlers=>[:erb, :builder, :raw, :ruby, :jbuilder, :haml]}. Searched in: 

The jbuilder views are working for other specs by using render_views. But when I add render_views to this spec, I get:

`method_missing': undefined local variable or method `render_views' for RSpec::ExampleGroups::UserEdit:Class (NameError) 

The difference between the specs where render_views works and this spec is the type. It's working here: describe SomeController, type: :controller do

But not on this one:
describe 'User edit', type: :request do

It's a request type since I'm testing the API response. As I said, I get the expected JSON view using curl from the command line, but it doesn't work in the tests. I must be missing some small detail or doing something completely wrong.

I also tried adding this to Rspec.configure but it didn't change anything:
config.render_views

Edit:

I must add the test pass when using: render json: { stuff }.to_json, status: :ok in the controller's response. This started failing when I refactored this into a jbuilder view.

Regarding the format, I'm using the 'simple_token_authentication' gem and passing this info to each request in the spec:

{ 'X-User-Email' => user.email, 'X-User-Token' => user.authentication_token, 'Content-Type' => 'application/json', 'Accept' => 'application/json' } 

I had format: :json in other tests and didn't make it work:

 post '/users/sign_in', @data, format: :json 

So setting format: :json as a value in the second parameter made things work.