This is the sample application for Ruby on Rails Tutorial: Learn Web Development with Rails by Michael Hartl. You can use this reference implementation to help track down errors if you end up having trouble with code in the tutorial. In particular, as a first debugging check I suggest getting the test suite to pass on your local machine:
cd /tmp
git clone https://github.com/ysiadf/sample_app_rails_4.git
cd sample_app_rails_4
cp config/database.yml.example config/database.yml
bundle install --without production
bundle exec rake db:migrate
bundle exec rake db:test:prepare
bundle exec rspec spec/
If the tests don't pass, it means there may be something wrong with your system. If they do pass, then you can debug your code by comparing it with the reference implementation.