```ruby
require 'test_helper'

module MyPlugin
  def self.configure(model)
    model.class_eval { attr_accessor :from_configure }
  end

  module ClassMethods
    def class_foo
      'class_foo'
    end
  end

  module InstanceMethods
    def instance_foo
      'instance_foo'
    end
  end
end

class PluginsTest < Test::Unit::TestCase
  context "plugin" do
    setup do
      @document = Class.new do
        extend MongoMapper::Plugins
        plugin MyPlugin
      end
    end

    should "include instance methods" do
      @document.new.instance_foo.should == 'instance_foo'
    end

    should "extend class methods" do
      @document.class_foo.should == 'class_foo'
    end

    should "pass model to configure" do
      @document.new.should respond_to(:from_configure)
    end

    should "default plugins to empty array" do
      Class.new { extend MongoMapper::Plugins }.plugins.should == []
    end

    should "add plugin to plugins" do
      @document.plugins.should include(MyPlugin)
    end
  end
end```

Fix test to use ActiveSupport::Concern
user
```ruby
require 'test_helper'

module MyPlugin
  extend ActiveSupport::Concern
  def self.configure(model)
    model.class_eval { attr_accessor :from_configure }
  end

  module ClassMethods
    def class_foo
      'class_foo'
    end
  end

  module InstanceMethods
    def instance_foo
      'instance_foo'
    end
  end
end

class PluginsTest < Test::Unit::TestCase
  context "plugin" do
    setup do
      @document = Class.new do
        extend MongoMapper::Plugins
        plugin MyPlugin
      end
    end

    should "include instance methods" do
      @document.new.instance_foo.should == 'instance_foo'
    end

    should "extend class methods" do
      @document.class_foo.should == 'class_foo'
    end

    should "pass model to configure" do
      @document.new.should respond_to(:from_configure)
    end

    should "default plugins to empty array" do
      Class.new { extend MongoMapper::Plugins }.plugins.should == []
    end

    should "add plugin to plugins" do
      @document.plugins.should include(MyPlugin)
    end
  end
end```
assistant