What should I do to make this rails app testable? - ruby-on-rails

Question

I have an up to date rails application, using rails 3.2 with mongoid 2. I was unable to start testing by typing rake. The exception thrown is (sanitized):
rake test
/railsapp/app/models/image.rb:18:in `<class:Image>': undefined method `[]' for nil:NilClass (NoMethodError)
from /railsapp/app/models/image.rb:1:in `<top (required)>'
from /gems/activesupport-3.2.8/lib/active_support/dependencies.rb:251:in `require'
from /gems/activesupport-3.2.8/lib/active_support/dependencies.rb:251:in `block in require'
from /gems/activesupport-3.2.8/lib/active_support/dependencies.rb:236:in `load_dependency'
from /gems/activesupport-3.2.8/lib/active_support/dependencies.rb:251:in `require'
from /gems/activesupport-3.2.8/lib/active_support/dependencies.rb:359:in `require_or_load'
from /gems/activesupport-3.2.8/lib/active_support/dependencies.rb:313:in `depend_on'
from /gems/activesupport-3.2.8/lib/active_support/dependencies.rb:225:in `require_dependency'
from /gems/railties-3.2.8/lib/rails/engine.rb:439:in `block (2 levels) in eager_load!'
from /gems/railties-3.2.8/lib/rails/engine.rb:438:in `each'
from /gems/railties-3.2.8/lib/rails/engine.rb:438:in `block in eager_load!'
from /gems/railties-3.2.8/lib/rails/engine.rb:436:in `each'
from /gems/railties-3.2.8/lib/rails/engine.rb:436:in `eager_load!'
from /gems/railties-3.2.8/lib/rails/application/finisher.rb:53:in `block in <module:Finisher>'
from /gems/railties-3.2.8/lib/rails/initializable.rb:30:in `instance_exec'
from /gems/railties-3.2.8/lib/rails/initializable.rb:30:in `run'
from /gems/railties-3.2.8/lib/rails/initializable.rb:55:in `block in run_initializers'
from /gems/railties-3.2.8/lib/rails/initializable.rb:54:in `each'
from /gems/railties-3.2.8/lib/rails/initializable.rb:54:in `run_initializers'
from /gems/railties-3.2.8/lib/rails/application.rb:136:in `initialize!'
from /gems/railties-3.2.8/lib/rails/railtie/configurable.rb:30:in `method_missing'
from /railsapp/config/environment.rb:7:in `<top (required)>'
from /railsapp/test/test_helper.rb:2:in `require'
from /railsapp/test/test_helper.rb:2:in `<top (required)>'
from /railsapp/test/unit/post_test.rb:1:in `require'
from /railsapp/test/unit/post_test.rb:1:in `<top (required)>'
from /gems/rake-0.9.2.2/lib/rake/rake_test_loader.rb:10:in `require'
from /gems/rake-0.9.2.2/lib/rake/rake_test_loader.rb:10:in `block (2 levels) in <main>'
from /gems/rake-0.9.2.2/lib/rake/rake_test_loader.rb:9:in `each'
from /gems/rake-0.9.2.2/lib/rake/rake_test_loader.rb:9:in `block in <main>'
from /gems/rake-0.9.2.2/lib/rake/rake_test_loader.rb:4:in `select'
from /gems/rake-0.9.2.2/lib/rake/rake_test_loader.rb:4:in `<main>'
Errors running test:units! #<RuntimeError: Command failed with status (1): [/Users/janlimpens/.rvm/rubies/ruby-1.9.3-p...]>
I created a gist with the files that are of interest in the context:
https://gist.github.com/3989760
There is no test concerning the image model at all, there are no fixtures and the only test I have got is included into the gist, but it is not to blame, the error is thrown upon including test_helper.rb.
What are my options?

Answer 1

When the tests start Rails loads up, as it does so it evaluates all of your models.
This includes the Image model, which apparently has a bug or typo on line 18.
Which would be this line:
:path => "#{APP_CONFIG['uploads_dir']}/:class/:id/:attachment/:style.:extension",
The only array notation here is:
APP_CONFIG['uploads_dir']
So, where is APP_CONFIG defined? And why is it a nil? These are the questions we must answer.
You might start by grepping your project for this string.