Ruby's require doesn't expand paths

January 9, 2008 popular , code 2 min read

I ran across this issue several weeks ago, but it came up at the latest Grand Rapids Ruby Group meeting, so I thought I would share it.

Ruby’s require, for better or worse, doesn’t expand paths. As the docs point out, require 'a'; require './a' will load a.rb twice. This doesn’t matter most of the time, but there’s one place it’s used often that will bite you: tests and specs.

Every Rails’ test has a line similar to this:

require File.dirname(__FILE__) + '/../test_helper'

This doesn’t normally cause any problems, as long as every test has an identical require statement. Where you start to get into problems is when you have tests in a nested subdirectory (like test/controllers/admin/users_controller_test.rb), in which case the require statement would look like this:

require File.dirname(__FILE__) + '/../../test_helper'

require sees this as a different file and will re-load it. This still shouldn’t hurt you unless you’re doing something in test_helper.rb that would be changed by loading it twice (like aliasing a method). This also effects RSpec with requiring spec_helper.rb

The solution? Expand the path yourself.

require File.expand_path(File.dirname(__FILE__) + '/../../test_helper')

It’s not really clear to me why Ruby’s require works this way. You would think a method that was intended to only load a file once would make sure that it never re-loaded the same file, no matter how it was referenced. It definitely doesn’t adhere to the “principle of least surprise”. Any idea why?

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