使用替代框架模拟

class Expector
  class << self
    def expectors
      @expectors ||= []
    end

    def clear_expectors
      expectors.clear
    end

    def verify_expectors
      expectors.each {|d| d.verify}
    end
  end

  def initialize
    self.class.expectors << self
  end

  def expectations
    @expectations ||= []
  end

  def expect(message)
    expectations << message.to_s
  end

  def verify
    unless expectations.empty?
      raise expectations.map {|e|
        "expected #{e}, but it was never received"
      }.join("\n")
    end
  end

private

  def method_missing(name, *args, &block)
    expectations.delete(name.to_s)
  end

public

  module RSpecAdapter
    def setup_mocks_for_rspec
      # no setup necessary
    end

    def verify_mocks_for_rspec
      Expector.verify_expectors
    end

    def teardown_mocks_for_rspec
      Expector.clear_expectors
    end
  end
end

require File.expand_path("../expector", __FILE__)

RSpec.configure do |config|
  config.mock_with Expector::RSpecAdapter
end

RSpec.describe Expector do
  it "passes when message is received" do
    expector = Expector.new
    expector.expect(:foo)
    expector.foo
  end

  it "fails when message is received" do
    expector = Expector.new
    expector.expect(:foo)
  end
end