There are many conceivable ways to organize the spec files. A graphical
representation of the Rubinius directories is shown below. This structure is
based on the Ruby language as well as the major components of a Ruby
implementation. The goal is to maintain locality by grouping related specs.

There are two primary divisions of the specs in the spec directory:
	1. specs for the Ruby language, which includes the Ruby core and standard
	   libraries;
	2. specs for the Rubinius system and its extensions to the Ruby core and
	   standard libraries.

spec
 |-- compiler
 |-- core
 |    +-- array
 |    +-- bignum
 |    +-- breakpoint
 |    +-- bytearray
 |    +-- ...
 |-- kernel
 |-- language
 |-- library
 |-- parser
 |-- ruby
 |    +-- command_line
 |    +-- core
 |          + -- array
 |          + -- bignum
 |          + -- binding
 |          + -- class
 |          + -- ...
 |          + -- time
 |          + -- true
 |          + -- unboundmethod
 |    +-- fixtures
 |    +-- language
 |    +-- library
 |          + -- enumerator
 |          + -- ...
 |          + -- time
 |          + -- yaml
 |    +-- ...
 |-- capi
 |     +-- ext
 +-- tags

The specs for the reference implementation of the Ruby language (MRI) are
under @spec/ruby@.  In the spec files under @spec/ruby@, there are also specs
for other Ruby implementations where these implementations comply with or
deviate from MRI (again, the reference implementation for Ruby).

All the spec directories except for spec/ruby are for Rubinius specific code.
Under spec/core, spec/language, and spec/libraries, there are specs for how
Rubinius extends or significantly deviates from MRI.

In general, there is no goal to unify spec/core, spec/language, and
spec/libraries with the parallel directories under spec/ruby/. These
directories serve different purposes.

For more information, please refer to:
  http://rubini.us/doc/en/specs/