xaviershay / ruby_interface.rb

Created June 05, 2011

# In ruby you can mock everything, but get no indication when you forget to change underlying methods.
# In Java, this would be picked up by the compiler.
# This makes mocking in ruby more fragile.
# What if you were only allowed to mock methods on an "interface"? In the simple case 
# this is just a class, but could be a module for re-use.
 
require 'minitest/unit'
require 'minitest/mock'
require 'minitest/autorun'
 
class UserDAO
  def update_email(email)
    # ...
  end
end
 
class UserUpdater
  def update_details(dao, attributes)
    dao.update_name_and_email(attributes[:name], attributes[:email])
  end
end
 
class InterfaceMock < MiniTest::Mock
  def initialize(interface)
    @interface = interface
    super()
  end
 
  def expect(method_name, *args)
    unless @interface.instance_methods(false).include?(method_name)
      raise "Attempted to stub #{method_name} which doesn't exist on #{@interface}"
    end
 
    super
  end
end
 
class UserUpdaterTest < MiniTest::Unit::TestCase
  def test_update_details_updates_email
    dao = InterfaceMock.new(UserDAO)
#     dao = MiniTest::Mock.new
    dao.expect(:update_name_and_email, nil, ['don', 'hello@example.com'])
    updater = UserUpdater.new
    updater.update_details(dao, name: 'don', email: 'hello@example.com')
    dao.verify
  end
end