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Senior QA Engineer - Desktop and Distributed Systems at Sur. Our Client is a US based security company looking for a Senior QA Engineer who thrives in complex, highly technical environments. . You will own end-to-end manual and automated testing, ensuring the distributed services and endpoint applications (built in .NET, C++, and React) are secure, reliable, and compatible. This is not a button-clicking QA role — they need someone who can reverse-engineer bugs, write integration test harnesses, validate stateful client/server behavior, and think like an attacker or power user.. What You Will Do:. . Define, own, and execute comprehensive test strategies across backend services, web frontends, and desktop apps on both Windows and macOS.. . Validate distributed system behaviors, including state synchronization, persistence, fault tolerance, and security guarantees.. . Create detailed, well-researched test plans and cases based on low-level system behavior, API contracts, and desktop workflows.. . Design and implement automation where appropriate (API/integration/UI level).. . Partner closely with development teams to catch issues early through ATDD or early exploratory testing.. . Contribute to reproducibility efforts for complex bugs (across platforms), including writing minimal repro apps or network mocks.. . Drive quality in high-scale systems composed of dozens of backend services and desktop agents.. . Maintain test environments and make sure they are evolving with requirements as they change.. . . 5+ years of QA experience, with significant time spent testing backend distributed systems, desktop apps, and full stack web apps.. . Strong hands-on experience testing Windows and macOS desktop applications, with a working knowledge of OS-level concepts like file systems, permissions, services, and sandboxing.. . Experience designing and running manual and automated tests for REST APIs, message queues, and background services.. . Understanding of .NET, C#, Win32 APIs, Swift, Objective-C, and modern web frameworks (like React) from a testing/debugging perspective.. . Familiarity with network protocols, security testing, or reverse engineering behavior at the application level.. . Experience using tools such as Charles/Fiddler, Wireshark, Postman, browser dev tools, or custom test harnesses.. . Comfortable with modern issue tracking, CI/CD, test management, and observability tools.. . Company Location: Argentina.