testing multiple models through same has_many :through assocation

assocation.rb

## I need to have a Group that can consist of Users and/or Companies

class User
  has_many :relationships
  has_many :companies, :through => :relationships
end

class Relationships
  belongs_to :user
  belongs_to :company
end

class Company
  has_many :relationships
  has_many :users, :through => :relationships
end

class Membership
  belongs_to :company
  belongs_to :user
  belongs_to :group
end

class Group
  has_many :memberships
  has_many :users, :through => :memberships
  has_many :companies, :through => :memberships
end