Use a constant to set the default batch size

Made the batch size a constant rather than a attribute to make it easier to read
and change later.

Through trial and error, I’ve hit upon a batch size of 3000 for one
month' data. This size could be larger for 7 days page views, and smaller for
one year’s page views.

app/models/importers/number_of_views_by_organisation.rb

@@ -1,10 +1,12 @@
 module Importers
   class NumberOfViewsByOrganisation
+    BATCH_SIZE = 3000
+
     def run(slug)
       organisation = Organisation.find_by(slug: slug)
       google_analytics_service = GoogleAnalyticsService.new
 
-      organisation.content_items.find_in_batches(batch_size: 1) do |content_items|
+      organisation.content_items.find_in_batches(batch_size: BATCH_SIZE) do |content_items|
         base_paths = content_items.pluck(:base_path)
 
         results = google_analytics_service.page_views(base_paths)

spec/models/importers/number_of_views_by_organisation_spec.rb

@@ -19,6 +19,9 @@
           },
         ]
       )
+
+      stub_const("Importers::NumberOfViewsByOrganisation::BATCH_SIZE", 1)
+
       subject.run('the-slug')
 
       content_item_one = ContentItem.find_by(base_path: 'the-link/first')
@@ -28,10 +31,22 @@
       expect(content_item_two.unique_page_views).to eq(2)
     end
 
-    it "perform the requests in batches" do
-      expect_any_instance_of(GoogleAnalyticsService).to receive(:page_views).twice.and_return([])
+    context "performs the request to google api in batches" do
+      it "makes two requests when the batch size is one" do
+        expect_any_instance_of(GoogleAnalyticsService).to receive(:page_views).twice.and_return([])
 
-      subject.run('the-slug')
+        stub_const("Importers::NumberOfViewsByOrganisation::BATCH_SIZE", 1)
+
+        subject.run('the-slug')
+      end
+
+      it "makes one request when the batch size is two" do
+        expect_any_instance_of(GoogleAnalyticsService).to receive(:page_views).once.and_return([])
+
+        stub_const("Importers::NumberOfViewsByOrganisation::BATCH_SIZE", 2)
+
+        subject.run('the-slug')
+      end
     end
   end
 end