This is the sample application for the 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 ~/workspace
$ git clone https://github.com/mhartl/sample_app_3rd_edition.git
$ cd sample_app_3rd_edition
$ bundle install
$ bundle exec rake db:migrate
$ bundle exec rake test

The repository also has chapter-specific branches with the state of the code at the end of each chapter. You can view them as follows:

$ git branch --all
  .
  .
  .
  remotes/origin/account-activation-password-reset
  remotes/origin/filling-in-layout
  remotes/origin/following-users
  remotes/origin/log-in-log-out
  remotes/origin/master
  remotes/origin/modeling-users
  remotes/origin/sign-up
  remotes/origin/static-pages
  remotes/origin/updating-users
  remotes/origin/user-microposts

To check out one of these chapter-specific branches, just use git checkout followed by the name without remotes/origin/:

$ git checkout log-in-log-out

This should help you track down any discrepancies between your code and the code in the tutorial.