Senior Performance Test Engineer

We are looking for a Senior Performance Test Engineer to take ownership of performance testing within an international project. In this role, you will drive the performance testing process end to end — from understanding business requirements and defining workload models through preparing test data and k6 scripts to test execution, results analysis and final recommendations.

• Owning performance testing end to end — from requirements and test-data preparation through execution, analysis and final reporting.
• Designing performance scenarios based on business requirements, including transactions per hour, load tiers and acceptance criteria.
• Building and maintaining performance test scripts using k6 and JavaScript.
• Selecting appropriate k6 workload models and executors for different performance scenarios.
• Testing REST API flows, including authentication, sessions and data correlation between individual steps.
• Preparing and validating test data, including CSV feeders and sensitive data.
• Running and parameterising performance tests through Azure DevOps Pipelines.
• Exporting and analysing performance metrics using Prometheus and Grafana.
• Correlating client-side test results with application and infrastructure metrics.
• Identifying bottlenecks, practical performance ceilings and the root causes of failures.
• Distinguishing between script, test-data, application, infrastructure and environment issues.
• Preparing clear performance reports and evidence-based recommendations for both technical and non-technical stakeholders.
• Identifying risks and blockers early and proposing appropriate mitigation.
• Coordinating performance-testing activities across Development, DevOps, QA and business teams and working closely with the Project Manager and Release Manager.
• Using AI tools to support script development, test-data preparation, log and result analysis and reporting while critically validating generated output.

• Strong hands-on experience with performance testing and independently driving performance-testing activities end to end.
• Strong practical knowledge of k6, including scripting, check(), metrics and thresholds.
• Solid understanding of k6 workload models and executors and the difference between VU-based and arrival-rate-based approaches.
• Good working knowledge of JavaScript (ES modules) for building and maintaining modular test scripts.
• Strong experience testing REST APIs, including HTTP methods, headers, session-token authentication and data correlation between requests.
• Ability to interpret HTTP and application-level error codes and identify the actual source of performance-test failures.
• Hands-on experience with Azure DevOps Pipelines, including running and parameterising tests, variables, conditions, artifacts and dedicated agents/pools.
• Practical experience with Prometheus and Grafana, including performance-metric analysis and correlation.
• Experience preparing and validating test data for performance testing.
• Ability to translate business requirements into meaningful performance scenarios, workload models and acceptance criteria.
• Strong analytical skills, including identifying bottlenecks, determining practical performance ceilings and distinguishing degradation from hard performance breaks.
• Strong troubleshooting skills and the ability to distinguish between script, data, application, infrastructure and environment issues.
• Experience producing clear performance reports and evidence-based recommendations without overinterpreting results.
• Ability to take ownership of the performance-testing area and coordinate activities across multiple teams and dependencies.
• Practical experience using AI tools to support performance-testing activities combined with the ability to critically validate AI-generated output.
• Basic knowledge of Git and feature-branch workflows.
• Strong written and spoken English, used comfortably in an international, cross-functional environment.
• Experience with Gatling.
• Experience working in closed or isolated environments without direct internet or npm access.
• Experience building and running prebuilt bundles, for example using esbuild.
• Experience performance testing banking or fintech systems.
• Experience with multi-country systems and country-specific configurations.
• Familiarity with user onboarding and authentication flows, including registration, verification, login and session management.

• We work in the latest technologies and with international clients, and our projects are polished from < to /> - learn about some of the projects we have completed.
• We organize TechTalks, meet-ups and create guilds where we exchange knowledge - you can learn a lot from your teammates.
• We have a close-knit team and we make sure to have regular integrations - we often go out to celebrate together.
• You can work remotely or choose to work from our offices in Wroclaw or Bielsko-Biala. However, we count on your openness to occasionally visit the office for team meetings or client visits, or possible occasional trips to the client's headquarters.
• You can adjust your working hours to suit your needs, starting your day between 7:00 and 10:00 am.
• You can work with great specialists in their fields who also have a sense of humor and other after-hours hobbies. It is the people who create the unique atmosphere and relaxed atmosphere at CSHARK.
• We have a flat structure - we are not a corporation and don't want to be one 🙃.
• We offer bonuses for employee referrals (from 3000 PLN to 7000 PLN).