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.

We are looking for someone who does more than simply run performance tests. You should be able to understand what the results actually tell us — determine the practical performance ceiling of a system, identify potential bottlenecks and distinguish infrastructure issues from application errors, test-data problems or issues within the test scripts themselves.

You will work with k6, JavaScript, Azure DevOps, Prometheus and Grafana, collaborating across Development, DevOps, QA and business teams. You will also work closely with the Project Manager and Release Manager while taking ownership of the overall performance testing area.

IN SHORT:🌎 100% REMOTELY or from one of our 2 offices💰 125 - 145 PLN/h + VAT☑️ B2B contract

Your Daily Missions

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.

The Essentials We’re Seeking

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.

Nice-to-haves

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.

Reasons Why You Would Enjoy Working With UsWe 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).