Fix invoice paying/fetching upcoming

Fixes #209

lib/stripe/invoice.rb

@@ -5,13 +5,12 @@ module Stripe
     include Stripe::APIOperations::Create
 
     def self.upcoming(params, opts={})
-      opts = Util.normalize_opts(opts)
-      response, api_key = Stripe.request(:get, upcoming_url, opts, params)
+      response, opts = request(:get, upcoming_url, params, opts)
       Util.convert_to_stripe_object(response, opts)
     end
 
-    def pay
-      response, opts = Stripe.request(:post, pay_url, @opts, {})
+    def pay(opts={})
+      response, opts = request(:post, pay_url, {}, opts)
       refresh_from(response, opts)
     end
 

test/stripe/invoice_test.rb

@@ -22,5 +22,19 @@ module Stripe
       i.pay
       assert_equal nil, i.next_payment_attempt
     end
+
+    should "pay with extra opts should pay an invoice" do
+      @mock.expects(:get).once.returns(test_response(test_invoice))
+      i = Stripe::Invoice.retrieve('in_test_invoice', {api_key: 'foobar'})
+
+      Stripe.expects(:execute_request).with do |opts|
+        opts[:url] == "#{Stripe.api_base}/v1/invoices/in_test_invoice/pay" &&
+          opts[:method] == :post &&
+          opts[:headers][:authorization] == 'Bearer foobar'
+      end.returns(test_response(test_paid_invoice))
+
+      i.pay
+      assert_equal nil, i.next_payment_attempt
+    end
   end
 end