RSpec matchers for direct assignment of attributes to an object

direct_assigment_matchers.rb

module DirectAssignmentMatchers
  require 'rspec/expectations'

  RSpec::Matchers.define :prevent_direct_assignment_of do |attribute|
    match do |object|
      !DirectAssignmentMatchers::public_assign(object, attribute)
    end
  end

  RSpec::Matchers.define :allow_direct_assignment_of do |attribute|
    match do |object|
      !!DirectAssignmentMatchers::public_assign(object, attribute)
    end
  end

  private

  def self.public_assign(object, attribute)
    begin
      object.public_send(:"#{attribute.to_s}=", 'test')
      true
    rescue NoMethodError
      false
    end
  end
end

RSpec.configure do |config|
  config.include DirectAssignmentMatchers
end