Senior API QA Engineer | Postman & Performance Testing

Senior API QA Engineer | Postman & Performance Testing
We are looking for an experienced QA Tester / API Test Engineer for a project focused on API migration, integration testing and UAT ownership.
Role: QA Tester / API Test Engineer
MD rate: 280 EUR / MD
Cooperation: Freelance / Contract
Key focus:
The ideal candidate will take ownership of API testing, performance testing, parity testing and UAT execution for B2B wholesale APIs.
Responsibilities:
Design, create and execute API test cases based on OpenAPI 3.0 specifications
Build and maintain complete Postman collections for Dev, UAT and Prod environments
Generate Newman HTML reports for UAT sign-off
Manage tokens, collection variables and environment variables in Postman
Create automated API tests using RestAssured, pytest-requests or similar tools
Handle complex API scenarios including correlation IDs, runtime-generated IDs, timestamps and multi-step business flows
Perform API parity testing between MuleSoft UAT and Quickwork UAT
Compare HTTP status codes, response schemas and field-level response data
Document expected differences versus actual defects
Work closely with MuleSoft SMEs to identify edge cases and DataWeave-specific behavior
Design and execute end-to-end business-flow tests, especially Feasibility → POQ → Order
Pass values such as feasibilityToken across multiple API calls
Prepare structured UAT reports with test cases, inputs, expected results, actual results, Pass/Fail status and supporting evidence
Required experience:
5+ years of API / integration testing experience
Strong hands-on Postman expertise
Experience with Newman reporting
Experience with Postman environments and collection variables
Programmatic API testing experience with RestAssured, pytest-requests or equivalent
Strong knowledge of test design techniques, including equivalence partitioning and boundary testing
Experience with contract testing / Pact is a strong advantage
Experience integrating Postman/Newman into GitLab CI/CD
Ability to ensure failed tests block the pipeline, not only generate reports
Performance testing is mandatory:
Hands-on experience with JMeter, k6 or Gatling
At least one completed end-to-end performance testing project
Ability to define baselines, ramp-up, sustained load and analyze results
Experience simulating realistic production traffic, including concurrent users, realistic request mix and think time
Ability to distinguish application latency, network latency and test-harness overhead
Ability to identify issues such as cold-start-related p95 spikes
Test data management:
Ability to create or source suitable test data for B2B wholesale APIs
Experience with synthetic test data based on TMF / MEF schemas is an advantage
No real customer or partner data should be used
We are looking for someone who can own the complete UAT test execution and provide a clear UAT Passed / Failed recommendation based on evidence.
Interested? Send me your CV or short profile.

Work arrangement
Yes