interface.feature

Feature: interfaces in Ruby
  As a developer that wants to use interfaces in Ruby,
  I want a DSL that emulates the following features:
    * interfaces are constantized
    * you cannot inherit from an interface
    * you cannot instanciate an interface
    * classes that implement interfaces MUST implement the methods defined in the interface
    * instances of classes that implement interfaces are of the kind of the interface names.

Background:
  Given a file named "i_have_an_account.rb" with:
    """ruby
    interface :iHaveAnAccount
      def account; end
    end
    """
  
  
Scenario: interfaces are constantized
  When I require "i_have_an_account.rb"
  Then the class IHaveAnAccount exists

Scenario: classes cannot inherit from an interface
  Given a file named "inherited_from_interface.rb" with:
  """ruby
  class InheritFromInterface < IHaveAnAccount
  end
  """
  
  When I require "i_have_an_account.rb"
  And I require "inherited_from_interface.rb"
  Then it should raise a RuntimeError

Scenario: interfaces cannot be instanciated
  When I require "i_have_an_account.rb"
  Then a new IHaveAnAccount should raise a RuntimeError

Scenario: classes that implement interfaces MUST implement the methods defined in the interface
  Given a file named "incomplete_invoice.rb" with:
  """ruby
  class IncompleteInvoice
    implements :iHaveAnAccount
  end
  """
  When I require "i_have_an_account.rb"
  And I require "incomplete_invoice.rb"
  then it should raise an ImplementationError

Scenario: classes that implement interfaces are of the kind of the interface
  Given a file named "invoice.rb" with:
  """ruby
    class Invoice
      implements :iHaveAnAccount

      def account
       'account'
      end
    end
  """
  When I require "invoice.rb"
  Then it should not raise an error
  And a new Invoice should be kind of IHaveAnAccount