Stubbing framework methods

purge_domain_users_spec.rb

# Poor specs
# ==========

describe PurgeDomainUsers do
  describe '.call' do
    # Test does not leave any freedom in implementation 
    it 'removes all users with email matching domain provided' do
      users = instance_double(:users_collection)
      allow(User).to receive(:where) { users }
      allow(users).to receive(:destroy_all)
      
      PurgeDomainUsers.call(domain: 'stark.com')
      
      expect(User).to have_received(:where).with('email ILIKE :domain_query', domain_query: "%@stark.com"))
      expect(users).to have_received(:destroy_all)
    end
  end
end

# Good specs
# ==========

describe PurgeDomainUsers do
  describe '.call' do
    it 'removes all users with email matching domain provided' do
      tony = create(:user, email: 'tony@stark.dev')
      create(:user, email: 'bruce@wayne.dev')
      howard = create(:user, email: 'howard@stark.dev')
      create(:user, email: 'peter@parker.dev')
      
      expect {
        PurgeDomainUsers.call(domain: 'stark.dev')
      }.to change { User.count }.from(4).to(2)
      
      expect { tony.reload }.to raise_error(ActiveRecord::RecordNotFound)
      expect { howard.reload }.to raise_error(ActiveRecord::RecordNotFound)
    end
  end
end

# Implementation
# ==============

class PurgeDomainUsers
  def self.call(domain:)
    User.
      where('email ILIKE :domain_query', domain_query: "%@#{domain}").
      destroy_all
  end
end