Ruby `reqrs` snippet

Ruby `reqrs` snippet inside a spec file, requires relative ruby source
file under test. Examples:
Spec File                   Snippet
'spec/lib/a_spec.rb'     => 'require_relative "../../lib/a"'
'spec/lib/a/b_spec.rb'   => 'require_relative "../../lib/a/b"'

There is a presumption that project code organization is idiomatic.
Source code directory struture mirrors specs directory structure.

The snippet is valuable for writing completely isolated unit tests.
In that case, you don't want to require 'spec_helper', but only ruby
class under test.