如何在Rails和RSpec中测试after_destroy回调？

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