Improve test coverage for the Views & Navigation processor

`ga_response_with_govuk_prefix` has not been used in any of the tests and
looks like it has been missed previously. We should expect paths that
contain the gov.uk prefix to be transformed into it's base path. If an
an event already exists with the same path in the Events::GA table, it
should update the entry with the aggregative total for the metrics which is
then reflected in the Facts::Metrics table.

spec/domain/etl/ga/views_and_navigation_processor_spec.rb

@@ -15,9 +15,7 @@
     before { allow(Etl::GA::ViewsAndNavigationService).to receive(:find_in_batches).and_yield(ga_response) }
 
     it "update the facts with the GA metrics" do
-      fact1 = create :metric,
-                     edition: edition1,
-                     date: "2018-02-20"
+      fact1 = create :metric, edition: edition1, date: "2018-02-20"
       fact2 = create :metric, edition: edition2, date: "2018-02-20"
 
       described_class.process(date:)
@@ -68,6 +66,58 @@
     end
   end
 
+  context "When the GA path contains the gov.uk prefix" do
+    before { allow(Etl::GA::ViewsAndNavigationService).to receive(:find_in_batches).and_yield(ga_response_with_govuk_prefix) }
+
+    context "when an event does not already exist with the same page_path" do
+      it "updates the fact with the GA metrics" do
+        fact1 = create :metric, edition: edition1, date: "2018-02-20"
+
+        described_class.process(date:)
+
+        expect(fact1.reload).to have_attributes(pviews: 1, upviews: 1)
+      end
+    end
+
+    context "when an event already exists with the same page_path" do
+      before do
+        create(:ga_event, :with_views, date: "2018-02-20", page_path: "/path1")
+      end
+
+      it "updates the fact with the aggregated GA metrics" do
+        fact1 = create :metric, edition: edition1, date: "2018-02-20"
+
+        described_class.process(date:)
+
+        expect(fact1.reload).to have_attributes(pviews: 11, upviews: 6)
+      end
+
+      it "does not update metrics for other days" do
+        fact1 = create :metric, edition: edition1, date: "2018-02-20", pviews: 20, upviews: 10
+
+        day_before = date - 1
+        described_class.process(date: day_before)
+
+        expect(fact1.reload).to have_attributes(pviews: 20, upviews: 10)
+      end
+
+      it "does not update metrics for other items" do
+        edition = create :edition, base_path: "/non-matching-path", date: "2018-02-20"
+        fact = create :metric, edition:, date: "2018-02-20", pviews: 99, upviews: 90
+
+        described_class.process(date:)
+
+        expect(fact.reload).to have_attributes(pviews: 99, upviews: 90)
+      end
+
+      it "deletes events after updating facts metrics" do
+        described_class.process(date:)
+
+        expect(Events::GA.count).to eq(0)
+      end
+    end
+  end
+
   it_behaves_like "traps and logs errors in process", Etl::GA::ViewsAndNavigationService, :find_in_batches
 
 private