Senior Software Development Engineer in Test (SDET)

Flex is a growth-stage, NYC headquartered FinTech company that is building the payment layer for life's financial obligations, giving households one place to see, split, and pay their bills around how they live and get paid. By offering greater choice over how and when payments are made and allowing eligible on time payments to help build a positive credit history, Flex puts households back in control of their cash flow.

That work brings together people with different perspectives who challenge the status quo and take ownership of solving difficult problems. For you, that means doing the best work of your career next to people who make you better, and together bringing ideas to life that make a real impact for the people we serve.

About the role

As a Senior SDET at Flex, you will own the test automation and quality efforts for entire product areas or major features. You will architect and optimize automation frameworks, lead test strategy for complex systems, and regularly collaborate across teams to deliver reliable and high-quality releases. This role offers the opportunity to mentor others, drive cross-functional quality improvements, and play a critical part in shaping the future of our engineering excellence.

What you’ll do

• Architect, implement, and optimize automated test frameworks for complex product areas, ensuring high reliability and maintainability

• Design, develop, and maintain robust automated test suites for API, UI, and integration testing, with Playwright as our primary end-to-end automation framework

• Design, build, and run performance, load, and stress tests using k6, defining performance baselines and thresholds for critical user flows and APIs

• Lead test strategy development and perform risk analysis for major features and systems

• Integrate automated testing, including performance tests with pass/fail thresholds, into CI/CD pipelines, supporting continuous integration and delivery processes

• Proactively identify systemic quality issues and drive cross-team process improvements to increase coverage and efficiency

• Analyze test coverage, identify gaps, and implement solutions to improve product quality

• Collaborate closely with engineering, product, and quality leaders on cross-functional quality initiatives and release planning

• Provide technical guidance and mentorship to junior SDETs and QA team members, fostering skill development and best practices

• Review code and test cases contributed by other engineers for quality and maintainability

• Maintain accurate and actionable test documentation, reports, and quality metrics for assigned product areas

• Investigate and resolve complex defects and production issues through advanced debugging and root cause analysis

• Advocate for quality and champion adoption of best practices within and across engineering teams

• Proven ability to lead test strategy and risk analysis while making high-impact technical decisions amid ambiguity and prioritizing what matters most.

Key qualifications

• Bachelor’s degree in Computer Science or related field, or equivalent experience

• 5+ years of experience in software development and test automation

• Advanced proficiency in multiple programming languages and test automation frameworks

• Deep experience designing, building, and maintaining automation frameworks (e.g., Playwright, Cypress, Selenium, RestAssured)

• Strong expertise in API, UI, and integration testing

• Strong, hands-on Playwright automation experience, including building scalable, maintainable, and stable suites (page objects, fixtures, parallelization, flaky-test reduction, and CI execution)

• Hands-on experience with performance and load testing using k6 (scripting scenarios, defining thresholds, and analyzing results to find bottlenecks) * Strong expertise in API, UI, and integration testing

• Proficient in CI/CD pipeline integration and optimization

• Skilled in test strategy development, risk analysis, and t...