add customer model spec and scope

app/controllers/customers_controller.rb

@@ -13,9 +13,9 @@ module DiscoursePatrons
           source: params[:source]
         )
 
-        DiscoursePatrons::Customer.create(
-          customer_id: customer.id
-          user_id: current_user.id
+        DiscoursePatrons::Customer.create_customer(
+          current_user,
+          customer
         )
 
         render_json_dump customer

app/models/customer.rb

@@ -2,6 +2,14 @@
 
 module DiscoursePatrons
   class Customer < ActiveRecord::Base
-    self.table_name = "discourse_patrons_customers"
+    scope :find_user, ->(user) { find_by_user_id(user.id) }
+
+    class << self
+      table_name = "discourse_patrons_customers"
+
+      def create_customer(user, customer)
+        create(customer_id: customer[:id], user_id: user.id)
+      end
+    end
   end
 end

db/migrate/20191025031631_create_customers.rb

@@ -6,6 +6,7 @@ class CreateCustomers < ActiveRecord::Migration[5.2]
       t.timestamps
     end
 
+    add_index :discourse_patrons_customers, :user_id, unique: true
     add_index :discourse_patrons_customers, :customer_id, unique: true
   end
 end

spec/models/customer_spec.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+module DiscoursePatrons
+  RSpec.describe Customer do
+    let(:user) { Fabricate(:user) }
+    let(:stripe_customer) { { id: 'cus_id4567' } }
+
+    it "has a table name" do
+      expect(described_class.table_name).to eq "discourse_patrons_customers"
+    end
+
+    it "creates" do
+      customer = described_class.create_customer(user, stripe_customer)
+      expect(customer.customer_id).to eq 'cus_id4567'
+      expect(customer.user_id).to eq user.id
+    end
+
+    it "has a user scope" do
+      described_class.create_customer(user, stripe_customer)
+      customer = described_class.find_user(user)
+      expect(customer.customer_id).to eq 'cus_id4567'
+    end
+  end
+end