Usage with validation_scopes

If you are using the excellent validation_scopes gem you'll find that it's not possible to use the shoulda matchers on the additional scopes.

This can be worked around with a bit of judicious monkey patching in a helper:

module ValidationScopesHelpers
  def rewire_errors_to_warnings(object)
    def object.valid?
      has_warnings?
    end

    def object.errors
      warnings
    end
  end
end

It's not the prettiest answer to this problem, but it does work! (extracted from here: https://github.com/thoughtbot/shoulda-matchers/issues/779#issuecomment-142329907)

Example

Say we want to test the validation in this ActiveRecord object:

class Obj < ActiveRecord::Base
  validates :name, presence: true

  validation_scope :warnings do |o|
    o.validates :address, presence: true
  end
end

The test case would look like this:

include ValidationScopesHelpers
subject(:obj) { FactoryBot.build :obj }

context "regular validation tests" do
  it { is_expected.to validate_presence_of(:name) }
end

context "validation warning tests" do
  before { rewire_errors_to_warnings(obj) }

  it { is_expected.to validate_presence_of(:address) }
end