rails - POST JSON in controller tests in rails 3.2.x - can't easily do it, necessary for things as simple as post body containing { action: "something" }

test.rb

# from http://stackoverflow.com/a/13206873/427710
env = Rack::MockRequest.env_for('/posts/1', :method => 'PUT', <some other params>)
status, headers, body = PostsController.action(:update).call(env)