# Mike Kostenko

**Java Software Engineer (Backend, Fintech)**

[contact@singledev.eu](mailto:contact@singledev.eu) · +351 913 602 401 · [linkedin.com/in/mike-kostenko](https://www.linkedin.com/in/mike-kostenko) · [github.com/vopros21](https://github.com/vopros21) · [singledev.eu](https://singledev.eu) · Porto, Portugal · EU work authorisation

## Summary

Java Software Engineer with 3+ years of backend and desktop development and 8 years in fintech at Devexperts (including 4+ years in QA). Oracle Certified Professional, Java SE 21. Core stack: Java 21, Spring, SQL/PostgreSQL, JUnit 5, Mockito, Swing, Git, CI/CD (GitHub Actions). Strong in testing, test performance and code review. Seeking senior backend roles, remote within the EU.

## Work Experience

### Java Developer, Devexperts – Porto, Portugal | Jan 2023 – Present

Developing and maintaining modules of a large-scale fintech platform across the lifecycle, from requirements to deployment.

- Cut unit test suite runtime by 83% by introducing concurrent test execution (Java concurrency, JUnit).
- Wrote the team's troubleshooting guide for unit test failures.
- Extended the corporate-actions pipeline (dividends, splits) to persist data in the database via a new DAO layer, following the legacy codebase's patterns and Spring wiring.
- Added unit tests for candle subscription-symbol logic (CandlePrice/CandleAlignment) edge cases.

- Analyse, estimate and implement backlog tasks; review pull requests for code quality and performance; support releases.
- Provide QA with functional context on code changes.

#### Internal platform: [Parking Service](https://singledev.eu/projects/parking.html) | 2025 – Present

- Designed, built and operate the office parking booking system used by ~80 employees (~100 bookings/week): half-day slots, waitlist queue, Slack notifications, admin audit log.
- Migrated it from managed cloud hosting to a self-hosted company Linux VM with PostgreSQL; set up automated daily backups, off-site copies and a tested restore procedure.
- Introduced spec-driven, AI-assisted development (Kiro): requirements, design and task breakdown, with characterization tests before refactoring core booking logic.

### QA Engineer, Devexperts – Porto, Portugal | Aug 2018 – Dec 2022

Ensuring quality and reliability of a complex fintech platform through structured testing and cross-team collaboration.

- Increased test coverage by 15% through automated tests (Python, Bash), significantly reducing manual effort.
- Key contributor in a team that met all critical deadlines for product launches.

- Wrote test cases and requirements docs, ran functional and regression testing, and automated QA tasks with Bash and Python.

## Projects

### [PNCT Territories Map](https://singledev.eu/projects/pnct.html) | Web app | 2026 – Present | TypeScript, MapLibre GL, Vite, Python, Playwright, Cloudflare Pages

Interactive map of Portugal's PNCT-eligible territories, with Idealista property-search links for each area.

### [HubitHab](https://singledev.eu/projects/hubithab.html) | iOS app | 2024 – Present | Swift, SwiftUI, HealthKit, Spring Boot

Automatic habit tracker: pulls activity from GitHub, LeetCode, HealthKit and X, with no manual logging.

## Skills

- **Languages:** Java (21), Swift, Groovy, Bash, Python, TypeScript
- **Frameworks:** Spring, Spring Boot, REST APIs, Swing, SwiftUI, picocli
- **Web:** Node.js, Fastify, React, MapLibre GL
- **Databases:** SQL, Oracle SQL, PostgreSQL, MySQL, SQLite, Liquibase
- **Testing:** JUnit 5, Mockito, TDD
- **Tools:** Git, Maven, Gradle, Continuous Integration/Delivery (CI/CD), GitHub Actions, Linux, JIRA, Splunk, IntelliJ IDEA, Xcode
- **Practices:** Agile/Scrum, Code review

## Certifications

- **Oracle Certified Professional (OCP): Java SE 21 Developer** – Oracle, Sep 2025
- **Courses:** GitHub Actions, GitHub Foundations (Microsoft Learn); 100 Days of SwiftUI (Hacking with Swift)

## Education

- **Master's degree** – Rostov State University of Transport Communication

## Languages

English (C1), Portuguese (A2)