This is a standard tree search kata, which has been done a lot of CW.

Needs sample tests.

No random tests.

Tests should use assert_equals.

Needs random tests

The tests should be augmented. The current tests don't seem to test (judging by accepted solutions) for the case when roles are not added implicitly to the role on which we call all_permissions, but only as sub-roles of other roles. E.g.:

can_edit = Permission.new 'Edit'
editors = Role.new 'Editor'
editors.permissions << can_edit

can_create = Permissions.new 'Create'
creators = Role.new 'Creator'
creators.permissions << can_create
creators.roles << editors

admins = Role.new 'Admin'
admins.roles << creators # Note that only creators are added explicitly, by editors is the sub-role of creators

Test.expect(admins.all_permissions.includes?(can_edit)) # Should include 'Edit' since 'Editors' are included in 'Creators'

Also, should test for circular references announces in the kata description ("A role can reference itself"). E.g., extending my example from above:

can_edit = Permission.new 'Edit'
editors = Role.new 'Editor'
editors.permissions << can_edit

can_create = Permissions.new 'Create'
creators = Role.new 'Creator'
creators.permissions << can_create
creators.roles << editors

admins = Role.new 'Admin'
admins.roles << creators
admins.roles << admins # circular reference!

Test.assert_equals( admins.all_permissions.map(&:name).sort, ['Create','Edit'] ) # Still should include the two permissions