add payment mode to conferences schema

spec/factories/conferences.rb

@@ -9,6 +9,7 @@ FactoryGirl.define do
     end_date { 6.days.from_now }
     registration_limit 0
     description { Faker::Hipster.paragraph }
+    payment_method 'offline'
 
     after(:create) do |conference|
       Role.where(name: 'organizer', resource: conference).first_or_create(description: 'For the organizers of the conference (who shall have full access)')

spec/models/conference_spec.rb

@@ -1545,6 +1545,20 @@ describe Conference do
       should validate_presence_of(:end_date)
     end
 
+    it 'is not valid without payment mode' do
+      should validate_presence_of(:payment_method)
+    end
+
+    it 'is valid with payment mode as Online' do
+      should allow_value('online').for(:payment_method).
+        with_message("'%{value}' is not a valid payment method")
+    end
+
+    it 'is valid with payment mode as Offline' do
+      should allow_value('offline').for(:payment_method).
+        with_message("'%{value}' is not a valid payment method")
+    end
+
     it 'is not valid with a duplicate short title' do
       should validate_uniqueness_of(:short_title)
     end