Add support for the LineItem resource and APIs (#918)

.travis.yml

@@ -17,7 +17,7 @@ sudo: false
 env:
   global:
     # If changing this number, please also change it in `test/test_helper.rb`.
-    - STRIPE_MOCK_VERSION=0.89.0
+    - STRIPE_MOCK_VERSION=0.90.0
 
 cache:
   directories:

lib/stripe/object_types.rb

@@ -49,6 +49,7 @@ def self.object_names_to_classes
         Issuing::Cardholder::OBJECT_NAME => Issuing::Cardholder,
         Issuing::Dispute::OBJECT_NAME => Issuing::Dispute,
         Issuing::Transaction::OBJECT_NAME => Issuing::Transaction,
+        LineItem::OBJECT_NAME => LineItem,
         LoginLink::OBJECT_NAME => LoginLink,
         Mandate::OBJECT_NAME => Mandate,
         Order::OBJECT_NAME => Order,

lib/stripe/resources.rb

@@ -38,6 +38,7 @@
 require "stripe/resources/issuing/cardholder"
 require "stripe/resources/issuing/dispute"
 require "stripe/resources/issuing/transaction"
+require "stripe/resources/line_item"
 require "stripe/resources/login_link"
 require "stripe/resources/mandate"
 require "stripe/resources/order"

lib/stripe/resources/checkout/session.rb

@@ -5,8 +5,11 @@ module Checkout
     class Session < APIResource
       extend Stripe::APIOperations::Create
       extend Stripe::APIOperations::List
+      extend Stripe::APIOperations::NestedResource
 
       OBJECT_NAME = "checkout.session"
+
+      nested_resource_class_methods :line_item, operations: %i[list]
     end
   end
 end

lib/stripe/resources/line_item.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+module Stripe
+  class LineItem < APIResource
+    OBJECT_NAME = "item"
+  end
+end

test/stripe/checkout/session_test.rb

@@ -36,6 +36,18 @@ class SessionTest < Test::Unit::TestCase
         assert_requested :get, "#{Stripe.api_base}/v1/checkout/sessions/cs_123"
         assert charge.is_a?(Stripe::Checkout::Session)
       end
+
+      context "#list_line_items" do
+        should "list the session's line items" do
+          sources = Stripe::Checkout::Session.list_line_items(
+            "cs_123"
+          )
+          assert_requested :get, "#{Stripe.api_base}/v1/checkout/sessions/cs_123/line_items"
+          assert sources.is_a?(Stripe::ListObject)
+          assert sources.data.is_a?(Array)
+          assert sources.data[0].is_a?(Stripe::LineItem)
+        end
+      end
     end
   end
 end

test/test_helper.rb

@@ -16,7 +16,7 @@
 require ::File.expand_path("stripe_mock", __dir__)
 
 # If changing this number, please also change it in `.travis.yml`.
-MOCK_MINIMUM_VERSION = "0.89.0"
+MOCK_MINIMUM_VERSION = "0.90.0"
 MOCK_PORT = Stripe::StripeMock.start
 
 # Disable all real network connections except those that are outgoing to