development.rb

config.after_initialize do
  MVOR::Gateway.use_3ds_test_gateway
end

mvor.rb

# config/initializers/mvor.rb

module MVOR

  module Gateway    
    def self.use_non_3ds_test_gateway
      Payment.gateway = ActiveMerchant::Billing::AxiarGateway.new(:login => 'test', :password => 'test', :mode => self.gateway_mode)
    end
  end
end

payment.rb

class Payment < ActiveRecord::Base
  belongs_to :order
  belongs_to :card
  delegate :scheme, :to => :card, :allow_nil => true

  cattr_accessor :gateway
  
  # ...
  private
    def get_gateway_response
      raise MVOR::Exception::GatewayNotConfigured, "Gateway has not been set" unless @@gateway
      #...
    end
end