Add common ThreadingHelper module for specs (#29116)

spec/services/resolve_account_service_spec.rb

@@ -219,27 +219,19 @@ RSpec.describe ResolveAccountService, type: :service do
   end
 
   it 'processes one remote account at a time using locks' do
-    wait_for_start = true
     fail_occurred  = false
     return_values  = Concurrent::Array.new
 
-    threads = Array.new(5) do
-      Thread.new do
-        true while wait_for_start
-
-        begin
-          return_values << described_class.new.call('foo@ap.example.com')
-        rescue ActiveRecord::RecordNotUnique
-          fail_occurred = true
-        ensure
-          RedisConfiguration.pool.checkin if Thread.current[:redis]
-        end
+    multi_threaded_execution(5) do
+      begin
+        return_values << described_class.new.call('foo@ap.example.com')
+      rescue ActiveRecord::RecordNotUnique
+        fail_occurred = true
+      ensure
+        RedisConfiguration.pool.checkin if Thread.current[:redis]
       end
     end
 
-    wait_for_start = false
-    threads.each(&:join)
-
     expect(fail_occurred).to be false
     expect(return_values).to_not include(nil)
   end