Ensure perform is idempotent

The important bit is idempotent anyway. This would
update timestamps and such, multiple times.

ee/spec/workers/geo/verification_worker_spec.rb

@@ -6,6 +6,7 @@ RSpec.describe Geo::VerificationWorker, :geo do
   include EE::GeoHelpers
 
   let(:package_file) { create(:conan_package_file, :conan_recipe_file) }
+  let(:job_args) { ['package_file', package_file.id] }
 
   describe '#perform' do
     it 'calls calculate_checksum!' do
@@ -14,17 +15,21 @@ RSpec.describe Geo::VerificationWorker, :geo do
 
       expect(replicator).to receive(:calculate_checksum!)
 
-      described_class.new.perform('package_file', package_file.id)
+      described_class.new.perform(*job_args)
     end
 
     context 'when on a primary node' do
       before do
         stub_primary_node
+        package_file.update!(verification_checksum: nil)
       end
 
-      it 'calculates the checksum' do
-        expect { described_class.new.perform('package_file', package_file.id) }
-          .to change { package_file.reload.verification_checksum }.from(nil)
+      it_behaves_like 'an idempotent worker' do
+        it 'calculates the checksum' do
+          described_class.new.perform(*job_args)
+
+          expect(package_file.reload.verification_checksum).to eq('ee66543d50acf8dfe39cbc0bbd40d4a801e479ecf5f90ebef9f2321eeb4bf09b')
+        end
       end
     end
   end