Require Error in test for a gem - ruby

Question

I have a project tree as below:
├── bin
├── fpgrowth-ruby-0.0.1.gem
├── fpgrowth-ruby.gemspec
├── Gemfile
├── Gemfile.lock
├── lib
│   ├── fpgrowth
│   │   ├── fptree
│   │   │   ├── builder
│   │   │   │   ├── first_pass.rb
│   │   │   │   └── second_pass.rb
│   │   │   ├── fp_tree.rb
│   │   │   └── node.rb
│   │   ├── models
│   │   │   └── transaction.rb
│   │   └── ruby
│   │   └── version.rb
│   └── fpgrowth.rb
├── LICENSE.txt
├── Rakefile
├── README.md
└── test
└── tc_first_pass.rb
In the TestCase for first_pass I wrote:
require 'test/unit'
require "../lib/fpgrowth/fptree/builder/first_pass"
Then I get this:
ruby test/tc_first_pass.rb
/home/damien/.rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- ../lib/fpgrowth/fptree/builder/first_pass (LoadError)
from /home/damien/.rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from test/tc_first_pass.rb:2:in `<main>'
Something is wrong, but I don't know what.

Answer 1

Use the -I flag on the ruby command line, to specify a require path at runtime.
from your top level directory
ruby -I lib test/tc_first_pass.rb
The above tells the ruby interpreter to include /lib in the load path for this execution only.
Then for your require line,
require 'fpgrowth/fptree/builder/first_pass'
For gem building, and organizing your source I suggest reading chapters on organizing your source, and distributing and packaging your code from the Programming Ruby book found here: http://pragprog.com/book/ruby3/programming-ruby-1-9

Answer 2

You can't require files like that unless you use require_relative.
Barring that, you should do is alter $LOAD_PATH to include ../lib.

Answer 3

You could use the File class-methods to help you.
First is to start off at the directory not relative to the cwd, but relative to the file calling the require. They might not be the same.
require File.dirname(__FILE__) + "../lib/fpgrowth/fptree/builder/first_pass"
This, however, is not very portable and can be cleaned up by using the join class-method:
require File.join(File.dirname(__FILE__), '..', 'lib', 'fpgrowth', 'fptree', 'builder', 'first_pass')
But you probably find yourself adding this all over the place, not? In that case, consider adding a helper in fpgrowth.rb:
def self.root
Pathname.new(File.expand_path(File.dirname(__FILE__)))
end
Now, you can use that helper all over the place:
FpGrowth.root #=> "/absolute/path/to/fpgrowth/lib"
FpGrowth.root.join("fpgrowth", "fbtree", "builder") #=> "/absolute/path/to/fpgrowth/lib/fpbrowth/fbtree/builder"