rspec and ActiveRecord::Base.transaction testing

model.rb

def set_new_name_on_items?
  success = ActiveRecord::Base.transaction do
    model.items.each do |i|
      i.name = 'new name'
      i.save or raise ActiveRecord::Rollback
    end
  !!success
end

model_spec.rb

it 'returns false on a single failing transaction' do
  items = [ item_a, item_b ]
  model = Fabricate(:model, items: items)
  item_b.stub(:save!).and_return(false)
  
  expect(model.set_new_name_on_items).to be false
end

it 'returns true on all save transaction' do
  items = [ item_a, item_b ]
  model = Fabricate(:model, items: items)

  expect(model.set_new_name_on_items).to be true
end

the spec was not passing since I stubbed item_b with: and_return(false). To get the transaction block to fail, the stub must be: and_raise(Error)

found a way to make the test work with and_return(false).

The important thing is to have raise ActiveRecord::Rollback within the ActiveRecord::Base.transaction so the every object in the transaction block is rolled back if any one of them errors. The previous example using save! worked, but if one transaction in the block saved successfully, it would not rollback if another failed.

actually, best way to stub this is: .stub(:create_or_update):
From the docs:

# File activerecord/lib/active_record/base.rb, line 2575
      def save
        create_or_update
      end

# File activerecord/lib/active_record/base.rb, line 2592
      def save!
        create_or_update || raise(RecordNotSaved)
      end

so, save and save! are slightly different but both call create_or_update.