QA / Test Engineer – API & Performance Testing

TalentLeader Human Resources Consultancy is looking for an experienced QA / Test Engineer on behalf of our client, with strong expertise in API integration testing, performance testing, and end-to-end test execution.
In this role, you will be responsible for validating API parity between different implementations, verifying performance requirements under production-like conditions, and owning User Acceptance Testing (UAT) throughout the migration process.
➡️ Position Details
• Start Date: ASAP
• Duration: Until 16 April 2027
• Workload: Full-time
• Location: Remote
➡️ Key Responsibilities
• Design and execute API parity tests by comparing MuleSoft and Quickwork implementations, validating HTTP status codes, response schemas, and semantic equivalence of response bodies.
• Develop and maintain API test suites using Postman/Newman and programmatic testing frameworks.
• Design and execute performance tests to validate production-like workloads, response times, throughput, and timeout requirements.
• Develop comprehensive test scenarios based on OpenAPI 3.0 specifications, covering boundary conditions, equivalence classes, optional and required field combinations, and error scenarios.
• Design and implement stateful end-to-end tests for the FPWP business flow: Feasibility → POQ → Order, including token propagation across multiple API requests.
• Develop regression test suites to ensure that API migration and cutover activities do not adversely affect existing integrations.
• Integrate automated API tests into GitLab CI/CD pipelines, ensuring that failed tests block the relevant pipeline stage.
• Own UAT execution, document test evidence and results, and provide clear pass/fail recommendations for formal sign-off.
• Collaborate with technical stakeholders and subject matter experts to investigate discrepancies, validate edge cases, and distinguish expected differences from defects.
• Prepare synthetic test data aligned with relevant B2B wholesale API schemas without exposing real customer or partner information.
➡️ Required Qualifications and Technical Skills
1️⃣ API Integration and Parity Testing
• At least 5 years of experience in API integration testing, including experience with API migration, re-platforming, or parallel implementation scenarios.
• Proven ability to validate parity between two implementations of the same API through systematic response comparison.
• Strong hands-on experience with Postman and Newman, including collection development, environment configuration, token management, automated execution, and HTML test reporting.
• Experience with RestAssured, pytest-requests, or an equivalent programmatic API testing framework.
• Understanding of contract testing principles; practical experience with Pact or similar tools is a strong advantage.
2️⃣ Performance Testing
• Hands-on experience with JMeter, k6, or Gatling, including baseline measurements, load ramp-up, sustained load testing, and performance result analysis.
• Ability to simulate realistic production traffic using concurrent users, representative request mixes, and appropriate think times.
• Understanding of application latency, network latency, test harness overhead, cold starts, and throughput limitations.
• Ability to identify the root causes of performance degradation and distinguish temporary latency spikes from genuine capacity constraints.
• Experience validating strict API timeout requirements under production-like load, including confirming that p99 response times remain below 55 seconds against a 60-second timeout constraint.
3️⃣ Test Design and Automation
• Strong knowledge of equivalence partitioning, boundary value analysis, negative testing, and regression test design.
• Ability to derive comprehensive test cases from OpenAPI 3.0 specifications, including edge cases beyond the examples explicitly provided.
• Experience designing and managing synthetic test data for B2B wholesale API integrations.
• Hands-on experience integrating Postman/Newman collections into GitLab CI/CD pipelines, with automated execution and pipeline-blocking failure conditions.
4️⃣ End-to-End Testing and UAT Ownership
• Experience designing stateful, multi-step API test scenarios involving token or identifier propagation across requests.
• Ability to determine when integration test scenarios require mocked backends and when live UAT integrations are necessary.
• Experience owning UAT execution and making evidence-based pass/fail recommendations.
• Ability to prepare structured test reports documenting test cases, inputs, expected results, actual results, and pass/fail status.
• Strong analytical, documentation, problem-solving, and stakeholder communication skills.
➡️ Nice-to-Have Qualifications
• Experience testing TM Forum Open APIs, particularly TMF622, TMF645, and TMF673.
• Familiarity with MEF Sonata APIs, including MEF87 POQ and MEF121 Address Validation.
• Experience testing Quickwork journeys through API triggers and inspecting execution traces in Quickwork logs.
• Practical experience with Pact or other contract testing solutions.
• German language skills for communicating test results to internal stakeholders.

Work arrangement
Yes