Rspec custom matcher

rspec_custojm_matcher.rb

#spec/support/model_helpers.rb
# use like this:
# it { is_expected.to have_validation ValidDatePresenceValidator,
#                                     :on => :start_date,
#                                     :options => [:allow_blank, :allow_nil]
#                                     }
RSpec::Matchers.define :have_validation do |validator, params|
  match do |model|
    my_validators = model.class.validators.select { |v| v.class == validator and v.attributes.include? params[:on] }
    my_validators = validators.select { |v| params[:options].all? { |po| v.options.any? { |vo| vo == po } } } if params[:options]
    my_validators.size == 1
  end

  failure_message do |model|
    message = "expected that #{model} would have validation #{validator} on '#{params[:on]}' field"
    message = message + " and options '#{params[:options]}'" if params[:options]
    message
  end

  failure_message_when_negated do |model|
    message = "expected that #{model} would NOT have validation #{validator} on '#{params[:on]}' field"
    message = message + " and options '#{params[:options]}'" if params[:options]
    message
  end
end


#TEST
#spec/models/validators/Rspec_support_model_helpers_spec.rb
 require 'rails_helper'

 describe "Rspec matchers" do
  let(:test_model) do
    Class.new do
      include ActiveModel::Validations

      attr_accessor :date_attr, :other_attr

      validates :date_attr, valid_date_presence: true
    end
  end

  subject { test_model.new }

  describe "should have a functional 'have_validation' matcher" do
    it { is_expected.to have_validation ValidDatePresenceValidator, :on => :date_attr }
    it { is_expected.to_not have_validation ValidDatePresenceValidator, :on => :other_attr }
  end
end