How to test after_destroy callback in Rails and RSpec? - ruby-on-rails

Question

I have this User class in Ruby on Rails:
class User < ActiveRecord::Base
after_destroy :ensure_an_admin_remains
private
def ensure_an_admin_remains
if User.where("admin = ?", true).count.zero?
raise "Can't delete Admin."
end
end
end
This works great and causes a database rollback if someone accidentally deletes an admin user.
The problem is that it seems to break the user delete action, even when testing with a non-admin user (generated by Factory Girl). This is my user_controller_spec.rb:
describe 'DELETE #destroy' do
before :each do
#user = create(:non_admin_user)
sign_in(#user)
end
it "deletes the user" do
expect{
delete :destroy, id: #user
}.to change(User, :count).by(-1)
end
end
Whenever I run this test, I get this error:
Failure/Error: expect{
count should have been changed by -1, but was changed by 0
There shouldn't be any error, though, because #user's admin attribute is set to false by default.
Can anybody help me out here?
Thanks...

Answer 1

I may be wrong but,
Your spec start with empty database right? So there is no admin user present in your db.
So when you call delete, you'll always have User.where("admin = ?", true).count equal to zero
Try creating an user admin before your test
describe 'DELETE #destroy' do
before :each do
create(:admin_user)
#user = create(:non_admin_user)
sign_in(#user)
end
it "deletes the user" do
expect{
delete :destroy, id: #user
}.to change(User, :count).by(-1)
end
end

Answer 2

I would make the following change:
before_destroy :ensure_an_admin_remains
def ensure_an_admin_remains
if self.admin == true and User.where( :admin => true ).count.zero?
raise "Can't delete Admin."
end
end

Answer 3

An alternative is to make the called function ensure_an_admin_remains a public function, such as check_admin_remains.
You can then test, the logic of check_admin_remains as if it were any other function.
Then in another test, you can ensure that function is called on destroy without any database interaction as follows:
let(:user) { build_stubbed(:user) }
it 'is called on destroy' do
expect(user).to receive(:check_admin_remains)
user.run_callbacks(:destroy)
end

Answer 4

You shouldn't raise for control flow. You can halt during callbacks to prevent the record being commited.
I've improved one some of the answers here for anyone else trying to work out how to do this properly as of Rails 5
class User < ActiveRecord::Base
before_destroy :ensure_an_admin_remains
private def ensure_an_admin_remains
return unless admin && User.where(admin: true).limit(2).size == 1
errors.add(:base, "You cannot delete the last admin.")
throw :abort
end
end