---
title: "Making race condition tests deterministic with Concurrent::CyclicBarrier and seam"
url: https://daily.dev/posts/making-race-condition-tests-deterministic-with-concurrent-cyclicbarrier-and-seam-mrundkise
source_url: https://blog.arkency.com/making-race-condition-tests-deterministic-with-cyclicbarrier-and-seam/
type: article
source: "arkency"
published: 2025-11-24T07:43:36.281Z
updated: 2025-11-24T07:43:58.004Z
tags: ["testing", "ruby", "rails"]
reading_time: 5
upvotes: 0
comments: 0
language: en
---

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# Making race condition tests deterministic with Concurrent::CyclicBarrier and seam

**[arkency](https://daily.dev/sources/arkency)** · 5 min read · 0 upvotes · 0 comments

## Summary

Demonstrates how to write deterministic tests for race conditions using Ruby's Concurrent::CyclicBarrier and the seam pattern from legacy code refactoring. Shows how to synchronize threads at specific points to reliably reproduce race conditions without modifying production code, using advisory locks as an example. The technique involves injecting a controlled projection that coordinates thread execution, making concurrent behavior testable and proving that concurrency protections like locks are actually necessary.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://blog.arkency.com/making-race-condition-tests-deterministic-with-cyclicbarrier-and-seam/>

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---

Tags: [#testing](https://daily.dev/tags/testing), [#ruby](https://daily.dev/tags/ruby), [#rails](https://daily.dev/tags/rails)

[View this post on daily.dev](https://daily.dev/posts/making-race-condition-tests-deterministic-with-concurrent-cyclicbarrier-and-seam-mrundkise)