Acts as Paranoid / Paranoia implementation for rails 4

paranoia.rb

# Copy of Paranoia gem without default_scope, which cannot be removed for assotiations
# in Rails 3.0. Refactored to use ActiveSupport::Concern, as it's only one file and don't need
# separate vendor/plugin.
module Paranoia
  extend ::ActiveSupport::Concern

  included do
    scope :deleted, ->{ where.not(deleted_at: nil) }
    scope :visible, ->{ where(deleted_at: nil) }
  end

  # Deletes the record in the database and freezes this instance to
  # reflect that no changes should be made (since they can't be
  # persisted). Returns the frozen instance.
  #
  # The row is simply removed with an SQL +DELETE+ statement on the
  # record's primary key, and no callbacks are executed.
  #
  # To enforce the object's +before_destroy+ and +after_destroy+
  # callbacks or any <tt>:dependent</tt> association
  # options, use <tt>#destroy</tt>.
  def delete
    self.update_attribute(:deleted_at, Time.now) if persisted? && !@destroyed
    @destroyed = true
    freeze
  end

  # Called by #destroy
  def destroy_row
    self.update_attribute(:deleted_at, Time.now)
  end

  def restore!
    update_attribute :deleted_at, nil
  end

  def destroyed?
    sync_with_transaction_state
    @destroyed || self.deleted_at.present?
  end

  def visible?
    !destroyed?
  end
end

paranoia_test.rb

require 'test_helper'

class TestModel < ActiveRecord::Base
  include Paranoia

  attr_accessor :stop_destroy
  before_destroy :bdestroy
  def bdestroy() !stop_destroy end
end

unless TestModel.table_exists?
  ActiveRecord::Migration.create_table :test_models do |t|
    t.string :string
    t.timestamp :deleted_at
  end
end

class ParanoiaTest < ActiveSupport::TestCase
  # Called before every test method runs.
  def setup
    @test_model = TestModel.create!(string: "test")
  end

  test "responds to visible?" do
    assert_respond_to @test_model, :visible?
  end

  test "adds scopes" do
    assert_respond_to TestModel, :visible
    assert_respond_to TestModel, :deleted
  end

  test "Model was created" do
    assert @test_model.persisted?
    assert !@test_model.destroyed?
  end

  test "destroying model without callbacks" do
    assert @test_model.destroy
    assert @test_model.destroyed?
    assert !@test_model.persisted?
    assert_kind_of Time, @test_model.deleted_at
  end

  test "deleting model" do
    assert @test_model.delete
    assert @test_model.destroyed?
    assert !@test_model.persisted?
    assert_kind_of Time, @test_model.deleted_at
  end

  test "Don't destroy model" do
    @test_model.stop_destroy = true
    assert !@test_model.destroy
    assert @test_model.persisted?
    assert_nil @test_model.deleted_at
  end

  # Called after every test method runs.
  def teardown
    TestModel.delete(@test_model.id)
  end
end