Senior Quality Assurance Engineer (Event Streaming)

We are looking for a Senior Quality Assurance Engineer (Event Streaming) to join our BUX team based in Amsterdam.

Our engineering team sits at the heart of the company. We have a well-rounded team that cares about building great products that matter. You'll be part of a modern fintech company where you can try things, break things, fix them, and learn fast. Your work is visible, your input matters, and you help shape both the product and how we build it. We stay close to what's happening in the world of investing and fintech, and we share what we learn. It's a place where you can stretch your skills, contribute to something real, and grow alongside people who take their craft seriously and enjoy building things together.

What you will do

In a fintech environment, reliable event streaming is critical; a missed or duplicated message can affect ledger balances, payment workflows, and compliance. You'll play a hands-on role in validating the correctness, reliability, and resilience of our Kafka-based event-driven systems.

As a Senior Quality Assurance Engineer for our Backend Broker team, your job is to get things done. This could mean:

• Design, develop, and maintain automated and manual tests for Kafka-based producers, consumers, and event flows

• Execute manual and exploratory testing where automation is not feasible

• Integrate automated regression, smoke, and integration test suites into CI/CD pipelines (GitHub Actions)

• Help build and mature QA processes and standards for event-driven systems within the squad

• Apply quality gates and acceptance criteria in close collaboration with Product and Development teams

• Participate in design reviews for owned features and event schemas to provide a QA perspective early in the development cycle

• Monitor and track key quality metrics, test coverage, and defect trends for the streaming domain

• Validate message ordering, delivery guarantees, idempotency, and exactly-once/at-least-once semantics

• Validate producer and consumer contracts and schema compatibility as services evolve

• Perform failure-mode and resilience testing - including broker failures, consumer lag, retries, dead-letter handling, and replay scenarios

• Perform bug triage, reproduction, and prioritization with development teams

• Support test environment setup, data provisioning, and maintenance in coordination with DevOps

• Use approved GenAI tooling with sanitized data to accelerate test design and automation, subject to human review, security policies, and validation of generated tests

Our tech stack

Java, Kotlin, Spring Boot, GCP, Kubernetes, GitHub Actions, Kafka, REST APIs, Selenium, Playwright/TypeScript, Postman/Newman, Charles Proxy, Xray, CloudSQL, PostgreSQL

What you need to succeed

We are looking for you if you are passionate about quality in distributed systems, you have strong hands-on testing skills across event-streaming platforms, and you thrive in a fast-paced fintech environment. Furthermore, we require:

• 5-7+ years of experience in software quality assurance, with a senior-level track record of hands-on testing in the fintech domain

• Hands-on testing experience with Kafka or comparable event-streaming platforms

• Strong knowledge of API testing (REST) and microservices/event-driven architectures

• Hands-on experience with test automation frameworks such as Selenium and Playwright with TypeScript

• Proficiency in at least one programming language (Java/Kotlin)

• Understanding of CI/CD pipelines and integration of automated tests (GitHub Actions)

• Practical experience with Postman/Newman, Charles Proxy, and Xray (or similar test management tooling)

• Comfortable validating data consistency across multiple database technologies and asynchronous event flows

• Experience helping establish or mature QA processes for event-driven systems

• Experience working in a fast-paced Agile environment

• Excellent communication and collaboration skills with cross-functional teams

• This role reports to the Staff QA Engineer

Nice-to-haves

• Experience with fintech or financial services testing (financial accuracy, transactional data, regulatory compliance)

• Experience with performance and security testing

• Knowledge of financial regulations and compliance standards (KYC/AML)

• Experience with schema registries and contract testing tools for event-driven architectures

Why join BUX as a Senior QA Engineer (Kafka)?

• You will have a real impact on quality for a high-growth fintech company that serves thousands of users

• You will work with event-streaming technologies that power our core trading and payment flows

• You'll collaborate with experienced, passionate engineers who value quality and continuous improvement

• You'll be part of a company that values your ideas and encourages innovation at every level

• You will help build products that democratize investing and make a real difference in people's financial lives