Restore versions DB table and add learning tests

test/learning/paper_trail_test.rb

@@ -0,0 +1,46 @@
+require 'test_helper'
+
+class Post < ActiveRecord::Base
+  has_paper_trail
+end
+
+class PaperTrailLearningTest < ActiveSupport::TestCase
+  setup do
+    ActiveRecord::Base.connection.create_table :posts do |t|
+      t.string :title
+
+      # Otherwise `touch_with_version` fails silently
+      t.datetime :updated_at
+    end
+  end
+
+  def test_returns_version_list
+    @record = Post.create!(title: 'any')
+
+    assert_equal 1, @record.versions.count
+    assert_respond_to @record.versions.first, :item_id
+  end
+
+  def test_creates_new_version_upon_update
+    @record = Post.create!(title: 'old title')
+    original_record = @record.clone
+
+    assert_difference -> { @record.versions.size } do
+      @record.update!(title: 'new title')
+    end
+    version = @record.versions.last
+    assert_equal @record.id, version.item_id
+    assert_equal @record.class.name, version.item_type
+    assert_equal version.reify, original_record
+    assert_equal ['old title', 'new title'], version.object_changes['title']
+    assert_equal 'update', version.event
+  end
+
+  def test_touch_with_version
+    @record = Post.create!(title: 'any')
+    
+    assert_difference -> { @record.versions.size } do
+      @record.touch_with_version
+    end
+  end
+end