Simple mock - lightweight mocking, supports method mocks, sequences, traits

_simple_mock.rb

class SimpleMock
  attr_reader :object

  @@mock_data = {}
  @@sequence ||= {}

  class << self
    def define name, &block
      @@mock_data[name] = block
    end

    def build *args
      object = new(*args).object
      yield object if block_given?
      object
    end

    def create *args
      object = build *args
      object.save
      yield object if block_given?
      object
    end
  end

  ###

  def initialize *args
    opts    = args.last.is_a?(Hash) ? args.pop : {}
    @klass  = args.shift
    @traits = args

    block = @@mock_data[@klass] || raise('object not defined')

    @object = @klass.to_s.classify.constantize.new
    instance_exec @object, &block

    raise 'Trait [%s] not found' % @traits.join(', ') if @traits.first

    opts.each { |k,v| @object.send("#{k}=", v) }
  end

  def trait(name, &block)
    if @traits.delete(name)
      instance_exec(@object, &block)
    end
  end

  def func(name, &block)
    @object.define_singleton_method(name, &block)
  end

  def sequence(name, start=nil)
    @@sequence[@klass] ||= {}
    @@sequence[@klass][name] ||= start || 0
    @@sequence[@klass][name] += 1
  end
end

mock-example.rb

require './config/application'
require 'simple_mock'
require 'faker'

SimpleMock.define :user do |u|
  u.name  = 'User %s' % sequence(:foo)
  u.email = Faker::Internet.email

  func :test1 do
    'foo bar custom: %s' % name
  end

  trait :bad_email do |o|
    o.email = 'Dux'
  end

  trait :overload do |o|
    func :name do
      'OVERLOADED'
    end
  end
end

user1 = SimpleMock.create(:user)
user2 = SimpleMock.create(:user, :bad_email)
user3 = SimpleMock.create(:user, name: 'Foo Barr')
user4 = SimpleMock.create(:user, :overload)

p user1.name # "User 1"
p user2.name # "User 2"
p user3.name # "Foo Barr"
p user4.name # "OVERLOADED"