Add spec file to test tracking history of embedded relations in parent

Demonstrates mongoid#187.

spec/integration/nested_embedded_documents_tracked_in_parent_spec.rb

@@ -0,0 +1,51 @@
+require 'spec_helper'
+
+describe Mongoid::History::Tracker do
+  before :all do
+    # Child model (will be embedded in Parent)
+    class Child
+      include Mongoid::Document
+      include Mongoid::History::Trackable
+
+      field :name
+      embedded_in :parent, inverse_of: :child
+    end
+
+    # Parent model (embeds one Child)
+    class Parent
+      include Mongoid::Document
+      include Mongoid::History::Trackable
+
+      field :name, type: String
+      embeds_one :child
+
+      track_history on: [:fields, :embedded_relations],
+                    version_field: :version,
+                    track_create: true,
+                    track_update: true,
+                    track_destroy: false
+    end
+  end
+
+  it 'should be able to track history for nested embedded documents in parent' do
+    p = Parent.new(name: 'bowser')
+    p.child = Child.new(name: 'todd')
+    p.save!
+
+    expect(p.history_tracks.length).to eq(1)
+    change = p.history_tracks.last
+    expect(change.modified['name']).to eq('bowser')
+    expect(change.modified['child']['name']).to eq('todd')
+
+    p.child.name = 'mario'
+    p.save!
+
+    expect(p.history_tracks.length).to eq(2)
+    expect(p.history_tracks.last.modified['child']['name']).to eq('mario')
+  end
+
+  after :all do
+    Object.send(:remove_const, :Parent)
+    Object.send(:remove_const, :Child)
+  end
+end