use short-form presence validator.

use two-argument form.
add unpaid scope.
repair tests.

spec/models/payment_spec.rb

@@ -7,33 +7,19 @@ describe Payment 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_expected.to validate_presence_of(:first_name) }
 
-    it 'is not valid without a last_name' do
-      should validate_presence_of(:last_name)
-    end
+    it { is_expected.to validate_presence_of(:last_name) }
 
-    it 'is not valid without a credit_card_number' do
-      should validate_presence_of(:credit_card_number)
-    end
+    it { is_expected.to validate_presence_of(:credit_card_number) }
 
-    it 'is not valid without a card_verification_value' do
-      should validate_presence_of(:card_verification_value)
-    end
+    it { is_expected.to validate_presence_of(:card_verification_value) }
 
-    it 'is not valid without a expiration_month' do
-      should validate_presence_of(:expiration_month)
-    end
+    it { is_expected.to validate_presence_of(:expiration_month) }
 
-    it 'is not valid without a expiration_year' do
-      should validate_presence_of(:expiration_year)
-    end
+    it { is_expected.to validate_presence_of(:expiration_year) }
 
-    it 'is not valid without a amount' do
-      should validate_presence_of(:amount)
-    end
+    it { is_expected.to validate_presence_of(:amount) }
 
     it 'is not valid with a amount equals zero' do
       should_not allow_value(0).for(:amount)

spec/models/ticket_spec.rb

@@ -108,11 +108,11 @@ describe Ticket do
              user: user,
              ticket: ticket,
              quantity: 20)
-      expect(ticket.quantity_bought_by(user, :paid => false)).to eq(20)
+      expect(ticket.quantity_bought_by(user, paid: false)).to eq(20)
     end
 
     it 'returns zero if the user has not bought this ticket' do
-      expect(ticket.quantity_bought_by(user, :paid => false)).to eq(0)
+      expect(ticket.quantity_bought_by(user, paid: false)).to eq(0)
     end
   end
 
@@ -122,11 +122,11 @@ describe Ticket do
              user: user,
              ticket: ticket,
              quantity: 20)
-      expect(ticket.total_price(user, :paid => false)).to eq(Money.new(100000, 'USD'))
+      expect(ticket.total_price(user, paid: 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, :paid => false)).to eq(Money.new(0, 'USD'))
+      expect(ticket.total_price(user, paid: false)).to eq(Money.new(0, 'USD'))
     end
   end
 
@@ -136,7 +136,7 @@ describe Ticket do
     describe 'user has bought' do
       context 'no tickets' do
         it 'returns zero' do
-          expect(Ticket.total_price(conference, user, :paid => false)).to eq(Money.new(0, 'USD'))
+          expect(Ticket.total_price(conference, user, paid: false)).to eq(Money.new(0, 'USD'))
         end
       end
 
@@ -146,7 +146,7 @@ describe Ticket do
         end
 
         it 'returns the correct total price' do
-          expect(Ticket.total_price(conference, user, :paid => false)).to eq(Money.new(100000, 'USD'))
+          expect(Ticket.total_price(conference, user, paid: false)).to eq(Money.new(100000, 'USD'))
         end
       end
 
@@ -158,7 +158,7 @@ describe Ticket do
 
         it 'returns the correct total price' do
           total_price = Money.new(200000, 'USD')
-          expect(Ticket.total_price(conference, user, :paid => false)).to eq(total_price)
+          expect(Ticket.total_price(conference, user, paid: false)).to eq(total_price)
         end
       end
     end