diff --git a/app/models/payment.rb b/app/models/payment.rb
index 5694303d..6d5a769f 100644
--- a/app/models/payment.rb
+++ b/app/models/payment.rb
@@ -47,7 +47,7 @@ class Payment < ActiveRecord::Base
     end
     unless response.success?
       errors.add(:base, response.message)
-      self.status = 2
+      self.status = 'failure'
       return false
     end
     self.user_id = user.id
diff --git a/spec/controllers/conference_registration_controller_spec.rb b/spec/controllers/conference_registration_controller_spec.rb
index 3c5655f0..d47d9271 100644
--- a/spec/controllers/conference_registration_controller_spec.rb
+++ b/spec/controllers/conference_registration_controller_spec.rb
@@ -42,7 +42,7 @@ describe ConferenceRegistrationsController, type: :controller do
 
         it 'does not assign price of purchased tickets to total_price and purchased tickets to tickets without payment' do
           expect(assigns(:total_price)).to eq Money.new(0, 'USD')
-          expect(assigns(:tickets)).not_to match_array [@purchased_ticket]
+          expect(assigns(:tickets)).not_to exist
         end
       end
 
diff --git a/spec/factories/payments.rb b/spec/factories/payments.rb
new file mode 100644
index 00000000..e4ccaee4
--- /dev/null
+++ b/spec/factories/payments.rb
@@ -0,0 +1,11 @@
+FactoryGirl.define do
+  factory :payment do
+    first_name { "#{Faker::Hipster.word} abc" }
+    last_name { "#{Faker::Hipster.word} xyz" }
+    credit_card_number { '4242424242424242' }
+    card_verification_value { '123' }
+    expiration_month { '06' }
+    expiration_year { Date.current.year + 2 }
+    amount { '10' }
+  end
+end
diff --git a/spec/models/conference_spec.rb b/spec/models/conference_spec.rb
old mode 100755
new mode 100644
diff --git a/spec/models/payment_spec.rb b/spec/models/payment_spec.rb
new file mode 100644
index 00000000..cd60b03f
--- /dev/null
+++ b/spec/models/payment_spec.rb
@@ -0,0 +1,117 @@
+require 'spec_helper'
+
+describe Payment do
+
+  describe 'validations' do
+    it 'has a valid factory' do
+      expect(build(:payment)).to be_valid
+    end
+
+    it 'is not valid without a first_name' do
+      should validate_presence_of(:first_name)
+    end
+
+    it 'is not valid without a last_name' do
+      should validate_presence_of(:last_name)
+    end
+
+    it 'is not valid without a credit_card_number' do
+      should validate_presence_of(:credit_card_number)
+    end
+
+    it 'is not valid without a card_verification_value' do
+      should validate_presence_of(:card_verification_value)
+    end
+
+    it 'is not valid without a expiration_month' do
+      should validate_presence_of(:expiration_month)
+    end
+
+    it 'is not valid without a expiration_year' do
+      should validate_presence_of(:expiration_year)
+    end
+
+    it 'is not valid without a amount' do
+      should validate_presence_of(:amount)
+    end
+
+    it 'is not valid with a amount equals zero' do
+      should_not allow_value(0).for(:amount)
+    end
+
+    it 'is not valid with a amount smaller than zero' do
+      should_not allow_value(-1).for(:amount)
+    end
+
+    it 'is valid with a amount greater than zero' do
+      should allow_value(1).for(:amount)
+    end
+
+  end
+
+  describe 'self#purchase' do
+    let!(:participant) { create(:user) }
+    let!(:ticket_1) { create(:ticket) }
+    let!(:ticket_2) { create(:ticket) }
+    let!(:conference) { create(:conference, tickets: [ticket_1, ticket_2]) }
+
+    it 'creates a purchase and payment for one ticket' do
+      tickets = { ticket_1.id.to_s => '1' }
+      message = TicketPurchase.purchase(conference, participant, tickets)
+      purchase = TicketPurchase.where(conference_id: conference.id,
+                                      user_id: participant.id,
+                                      ticket_id: ticket_1.id).first
+
+      expect(TicketPurchase.count).to eq(1)
+      expect(purchase.quantity).to eq(1)
+      expect(message.blank?).to be true
+
+      response = Payment.purchase(participant, conference, 1000)
+      payment = Payment.where(conference_id: conference.id,
+                              user_id: participant.id)
+
+      expect(Payment.count).to eq(1)
+      expect(payment.amount).to eq(10)
+      expect(response.blank?).to be true
+    end
+
+    it 'creates several purchases for more than one ticket' do
+      tickets = { ticket_1.id.to_s => '1', ticket_2.id.to_s => '1' }
+      message = TicketPurchase.purchase(conference, participant, tickets)
+      purchase_1 = TicketPurchase.where(conference_id: conference.id,
+                                        user_id: participant.id,
+                                        ticket_id: ticket_1.id).first
+
+      purchase_2 = TicketPurchase.where(conference_id: conference.id,
+                                        user_id: participant.id,
+                                        ticket_id: ticket_2.id).first
+
+      expect(TicketPurchase.count).to eq(2)
+      expect(purchase_1.quantity).to eq(1)
+      expect(purchase_2.quantity).to eq(1)
+      expect(message.blank?).to be true
+
+      response = Payment.purchase(participant, conference, 2000)
+      payment = Payment.where(conference_id: conference.id,
+                              user_id: participant.id)
+
+      expect(Payment.count).to eq(1)
+      expect(payment.amount).to eq(20)
+      expect(response.blank?).to be true
+    end
+
+    it 'creates no ticket purchase or payment if amount is less than 1' do
+      tickets = { ticket_1.id.to_s => '-1' }
+      TicketPurchase.purchase(conference, participant, tickets)
+
+      expect(TicketPurchase.count).to eq(0)
+    end
+
+    it 'creates no ticket purchase or payment if amount is 0' do
+      tickets = { ticket_1.id.to_s => '0' }
+      TicketPurchase.purchase(conference, participant, tickets)
+
+      expect(TicketPurchase.count).to eq(0)
+    end
+  end
+end
diff --git a/spec/models/ticket_spec.rb b/spec/models/ticket_spec.rb
index 496037ec..f6b5cd7f 100644
--- a/spec/models/ticket_spec.rb
+++ b/spec/models/ticket_spec.rb
@@ -82,17 +82,37 @@ describe Ticket do
     end
   end
 
+  describe '#unpaid?' do
+    let!(:ticket_purchase) { create(:ticket_purchase, user: user, ticket: ticket) }
+
+    context 'user has not paid' do
+      before { ticket_purchase.update_attributes(paid: false) }
+
+      it 'returns true' do
+        expect(ticket.unpaid?(user)).to eq(true)
+      end
+    end
+
+    context 'user has paid' do
+      before { ticket_purchase.update_attributes(paid: true) }
+
+      it 'returns false' do
+        expect(ticket.unpaid?(user)).to eq(false)
+      end
+    end
+  end
+
   describe '#quantity_bought_by' do
     it 'returns the correct value if the user has bought this ticket' do
       create(:ticket_purchase,
              user: user,
              ticket: ticket,
              quantity: 20)
-      expect(ticket.quantity_bought_by(user, 'f')).to eq(20)
+      expect(ticket.quantity_bought_by(user, false)).to eq(20)
     end
 
     it 'returns zero if the user has not bought this ticket' do
-      expect(ticket.quantity_bought_by(user, 'f')).to eq(0)
+      expect(ticket.quantity_bought_by(user, false)).to eq(0)
     end
   end
 
@@ -102,11 +122,11 @@ describe Ticket do
              user: user,
              ticket: ticket,
              quantity: 20)
-      expect(ticket.total_price(user, 'f')).to eq(Money.new(100000, 'USD'))
+      expect(ticket.total_price(user, false)).to eq(Money.new(100000, 'USD'))
     end
 
     it 'returns zero if the user has not bought this ticket' do
-      expect(ticket.total_price(user, 'f')).to eq(Money.new(0, 'USD'))
+      expect(ticket.total_price(user, false)).to eq(Money.new(0, 'USD'))
     end
   end
 
@@ -116,7 +136,7 @@ describe Ticket do
     describe 'user has bought' do
       context 'no tickets' do
         it 'returns zero' do
-          expect(Ticket.total_price(conference, user, 'f')).to eq(Money.new(0, 'USD'))
+          expect(Ticket.total_price(conference, user, false)).to eq(Money.new(0, 'USD'))
         end
       end
 
@@ -126,7 +146,7 @@ describe Ticket do
         end
 
         it 'returns the correct total price' do
-          expect(Ticket.total_price(conference, user, 'f')).to eq(Money.new(100000, 'USD'))
+          expect(Ticket.total_price(conference, user, false)).to eq(Money.new(100000, 'USD'))
         end
       end
 
@@ -138,7 +158,7 @@ describe Ticket do
 
         it 'returns the correct total price' do
           total_price = Money.new(200000, 'USD')
-          expect(Ticket.total_price(conference, user, 'f')).to eq(total_price)
+          expect(Ticket.total_price(conference, user, false)).to eq(total_price)
         end
       end
     end