Using log_in_as helper module in ActionDispatch::IntegrationTest - ruby-on-rails-4

Question

I started learning Rails using Michael Hartl's "Ruby on Rails Tutorial", then I started to customize some classes to suit my own needs.
At this time, I have 2 main classes I can manage with my application:
"users": admin user can list, create destroy them
"apps": admin can list, create destroy them
I recycled most from the tutorial, and managed to make the application working for both of them.
"users" integration testing works fine.
When started to develop the "apps" testing, I found there is something that makes login fail and I'm really stucked on this.
Here is the "users" integration test (it works):
require 'test_helper'
class UsersCreateTest < ActionDispatch::IntegrationTest
fixtures :all
def setup
#admin = users(:admin)
end
test "user create with valid information" do
log_in_as(#admin)
assert is_logged_in?
get new_user_path()
...
assert_difference 'User.count', 1 do
post users_path, user:{ username: "newuser",
email: "user#example.com",
password: "pippo1",
password_confirmation: "pippo1",
...
}
follow_redirect!
end
...
end
end
Here is the test to create a new "app" (does not work):
require 'test_helper'
class AppsCreateTest < ActionDispatch::IntegrationTest
fixtures :all
def setup
#admin= users(:admin)
#app= apps(:app1)
end
test "create app with valid information" do
log_in_as(#admin)
assert is_logged_in?
get new_app_path()
...
assert_difference( 'App.count', 1) do
post apps_path, app: { appname: "newapp",
desc: "short descprition here",
...
}
follow_redirect!
end
end
end
Finally, here is the "test_helper.rb" part, which comes straight from the Hartl Tutorial:
ENV['RAILS_ENV'] ||= 'test'
require File.expand_path('../../config/environment', __FILE__)
require 'rails/test_help'
class ActiveSupport::TestCase
# Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
fixtures :all
def is_logged_in?
!session[:user_id].nil?
end
# Logs in a test user.
def log_in_as(user, options = {})
password= options[:password] || 'pippo1'
if integration_test?
post "/login", session: {
username: user.username,
password: password }
else
session[:user_id] = user.id
end
end
private
# Returns true inside an integration test.
def integration_test?
defined?(post_via_redirect)
end
end
The "app" test fails when it tries to do post operation in "log_in_as".
It seems that the "user" test inherits some method while the "app" test doesn't.
Any suggestion is appreciated.