Hello,
Is this a desired behavior to have:

class House
include Mongoid::Document
has_many :windows
end

class Window
include Mongoid::Document
belongs_to :house
end

and

it 'adds windows to the relation' do
house = House.new
house.save!
window = Window.new(:house => house)
expect(house.windows).to include window
end

it 'adds windows to the relation' do
house = House.new
house.save!
window = Window.new
house.windows << window
expect(house.windows).to include window
end

to both pass yet,

it 'persists windows' do
house = House.new
house.save!
expect

{ house.windows << Window.new }

.to change(Window, :count).by(1)
end

passes and

it 'persists windows' do
house = House.new
house.save!
expect

{ Window.new(:house => house) }

.to change(Window, :count).by(1)
end

fails ?