Add worker spec

spec/workers/issue_rebalancing_worker_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IssueRebalancingWorker do
+  describe '#perform' do
+    it 'runs an instance of IssueRebalancingService' do
+      issue = create(:issue)
+
+      service = double(execute: nil)
+      expect(IssueRebalancingService).to receive(:new).with(issue).and_return(service)
+
+      described_class.new.perform(issue.id)
+    end
+  end
+end