currency of a single ticket could be updated now

closes #1913

fixed travis faliures

minor changes

removed empty file

added tests regarding currency updation

app/models/ticket.rb

@@ -76,7 +76,9 @@ class Ticket < ApplicationRecord
   private
 
   def tickets_of_conference_have_same_currency
-    unless Ticket.where(conference_id: conference_id).all?{|t| t.price_currency == price_currency }
+    tickets = Ticket.where(conference_id: conference_id)
+    return if tickets.count.zero? || (tickets.count == 1 && self == tickets.first)
+    unless tickets.all?{|t| t.price_currency == price_currency }
       errors.add(:price_currency, 'is different from the existing tickets of this conference.')
     end
   end

spec/models/ticket_spec.rb

@@ -6,6 +6,7 @@ describe Ticket do
   let(:user) { create(:user) }
 
   describe 'validation' do
+
     it 'has a valid factory' do
       expect(build(:ticket)).to be_valid
     end
@@ -177,4 +178,25 @@ describe Ticket do
       end
     end
   end
+
+  describe 'currency updation' do
+    context 'when more than one ticket exist for a conference' do
+      it 'should not allow currency update' do
+        ticket.update(price_currency: 'INR')
+        expected_error_message = 'Price currency is different from the existing tickets of this conference.'
+        expect(ticket.errors.full_messages).to eq([expected_error_message])
+      end
+    end
+
+    context 'when a single ticket exists for a conference' do
+      before do
+        ticket.destroy
+      end
+
+      it 'should allow currency update' do
+        free_ticket = Ticket.first
+        expect { free_ticket.update_attributes(price_currency: 'INR') }.to change { free_ticket.reload.price_currency }.from('USD').to('INR')
+      end
+    end
+  end
 end