Implement remaining_budget? method in discount budget

lib/planet_express/discount_budget.rb

@@ -19,6 +19,10 @@ module PlanetExpress
       budget - spent_budget
     end
 
+    def remaining_budget?
+      !available_budget.zero?
+    end
+
     private
 
     attr_reader :applied_discounts

spec/discount_budget_spec.rb

@@ -9,6 +9,7 @@ RSpec.describe PlanetExpress::DiscountBudget do
       it 'returns the full discount' do
         expect(subject.apply_discount(120)).to eq(120)
         expect(subject.available_budget).to eq(380)
+        expect(subject.remaining_budget?).to eq(true)
       end
     end
 
@@ -16,6 +17,7 @@ RSpec.describe PlanetExpress::DiscountBudget do
       it 'returns only the remaining budget' do
         expect(subject.apply_discount(650)).to eq(500)
         expect(subject.available_budget).to eq(0)
+        expect(subject.remaining_budget?).to eq(false)
       end
     end
   end