Why I am not able to run rails tests - ruby-on-rails

Question

This is what I did.
> git clone git://github.com/rails/rails.git
> cd rails
> cd railties
> rake
And I got following error.
(in /Users/dorelal/dev/scratch/rails/railties)
./test/isolation/abstract_unit.rb:236:in `initialize': No such file or directory - /Users/dorelal/dev/scratch/rails/railties/tmp/app_template/config/boot.rb (Errno::ENOENT)
from ./test/isolation/abstract_unit.rb:236:in `open'
from ./test/isolation/abstract_unit.rb:236
from ./test/isolation/abstract_unit.rb:222:in `initialize'
from ./test/isolation/abstract_unit.rb:222:in `new'
from ./test/isolation/abstract_unit.rb:222
from test/application/configuration_test.rb:1:in `require'
from test/application/configuration_test.rb:1
rake aborted!
I checked ~/railties/tmp and this directory is empty.
I know rails is not broken. So what am I missing?

Answer 1

You need to run bundle install after you cd rails. That will install all the gems required by your new Rails repo, including minitest (test-unit at the time of your question.)
After you run bundle install, you will be able to run the rails tests by doing a cd into the component directory and then either running the entire test suite for that component, or specifying a single test file, as follows (using actionpack as an example):
To run all tests for actionpack:
cd actionpack
TEST_DIR=generators bundle exec rake test
To run the tests for actionpack test/dispatch/rack_test.rb:
cd actionpack
bundle exec ruby -Itest test/dispatch/rack_test.rb
To run the entire test suite for all of rails:
cd rails
bundle exec rake test
A Necromancer cannot resist such a question - so old, yet so relevant, so cleanly asked, so not documented properly.