test invoice model

app/models/invoice.rb

@@ -10,6 +10,8 @@ class Invoice < ApplicationRecord
   end
 
   def serialize_order
-    self.data ||= Invoice::OrderSerializer.new(order).serializable_hash
+    return data unless data.empty?
+
+    self.data = Invoice::OrderSerializer.new(order).serializable_hash
   end
 end

spec/models/invoice_spec.rb

@@ -3,5 +3,19 @@
 require 'spec_helper'
 
 RSpec.describe Invoice, type: :model do
-  pending "add some examples to (or delete) #{__FILE__}"
+  describe 'presenter' do
+    it 'should return an instance of Invoice::DataPresenter' do
+      invoice = create(:invoice)
+      expect(invoice.presenter).to be_a(Invoice::DataPresenter)
+    end
+  end
+
+  describe 'serialize_order' do
+    let!(:distributor) { create(:distributor_enterprise) }
+    let!(:order) { create(:order, :with_line_item, :completed, distributor: distributor) }
+    it 'serializes the order' do
+      invoice = create(:invoice, order: order)
+      expect(invoice.data).to eq(Invoice::OrderSerializer.new(order).serializable_hash)
+    end
+  end
 end