rails-concern

Extracting duplicated Rails model logic into a reusable module involves creating an ActiveSupport::Concern. This Skill scaffolds the concern alongside RSpec tests, ensuring shared validations, callbacks, or scopes are safely refactored without breaking existing functionality.

Testing shared Rails concerns with RSpec is best achieved through a tests-first workflow. By writing failing specs for the desired behavior before implementation, you ensure the extracted ActiveSupport::Concern module functions correctly when mixed into models or controllers.

Yes, you can use Rails concerns to share behavior across both models and controllers. The generator handles scaffolding for both ActiveSupport::Concern model modules and controller concerns, allowing you to extract duplicated helpers or logic into shared code.

To start refactoring a Rails app using a test-driven approach, write a failing RSpec spec for the desired shared behavior first. Then, generate the concern module to scaffold the implementation, ensuring your refactoring safely extracts duplicated logic.

You should avoid using ActiveSupport::Concern for modular design when the duplicated logic is minimal or highly specific to a single class. Overusing concerns can obscure code flow, so reserve them for extracting genuinely shared validations, callbacks, or helpers across multiple models.