Custom validator on associated model make other Rspec model tests break - ruby-on-rails

Question

I have 2 models sharing a simple belong_to/has_many relation: Room belongs to Building
I created a custom validator called total_number_rooms_limited_to_15 that ensures I can't create more than 15 rooms for a given Building.
class Room < ActiveRecord::Base
# -- Relationships --------------------------------------------------------
belongs_to :admin_user, :foreign_key => 'admin_user_id'
belongs_to :building, :foreign_key => 'building_id'
# -- Validations ----------------------------------------------------------
validates :room_filename,
presence: true
# associated models primary key validates
validates :admin_user_id,
presence: true
validates :building_id,
presence: true
validate :total_number_rooms_limited_to_15
private
def total_number_rooms_limited_to_15
errors[:base] << "There can't be more than 15 rooms. There are already 15 .
<br/>Please remove another one or drop trying adding this one.".html_safe
unless ( self.building.rooms.count < 15 )
end
But the problem is that after creating this new validator, all my "usual" basic tests fail.
require 'spec_helper'
RSpec.describe Room, type: :model do
before(:each) do
#attr = {
room_filename: "xyz"
}
end
# -- Models Tests --------------------------------------------------------
describe "tests on ST's models validations for room_filename" do
it { is_expected.to validate_presence_of(:room_filename) }
it { is_expected.not_to allow_value(" ").for(:room_filename) }
end
All give me the following error message:
1) Room tests on ST's models validations for room_filename should validate that :room_filename cannot be empty/falsy
Failure/Error:
errors[:base] << "There can't be more than 15 rooms. There are already 15 .
<br/>Please remove another one or drop trying adding this one.".html_safe unless ( self.building.rooms.count < 15 )
NoMethodError:
undefined method `rooms' for nil:NilClass
I tried adding inside #attr the attribute a associated "virtual" building but it not work out;, getting the same error message:
before(:each) do
#attr = {
room_filename: "xyz",
building_id: 1
}
ADDED INFO
config.before(:suite) do
DatabaseCleaner.clean_with(:truncation, :except => %w(roles))
end
config.before(:each) do
DatabaseCleaner.strategy = :transaction
end
config.before(:each, js: true) do
DatabaseCleaner.strategy = :truncation
end
config.before(:each) do
DatabaseCleaner.start
end
config.after(:each) do
DatabaseCleaner.clean
end

Answer 1

For custom validations you'll need to instantiate a new Room object in your tests. If you don't have something like factory_girl or fabrication in place to create objects for your test, you can do this:
before(:each) do
#admin_user = AdminUser.create!(...attributes)
#building = Building.create!(...attributes)
#room = Room.create!(building_id: #building.id, admin_user_id: #admin_user.id)
end
Then make sure you're calling your validation on the instance instead of your Room class:
def total_number_rooms_limited_to_15
errors[:base] << "There can't be more...".html_safe
unless ( building.present? && building.rooms.count < 15 )
end