Senior Software Development Engineer in Test (SDET)

Flex is a growth-stage, NYC headquartered FinTech company that is creating the best rent payment experience. It’s hard to believe that it’s 2026 and paying rent on time is expensive, inflexible, and difficult. We’re here to change that! Flex enables our users to pay rent throughout the month on a schedule that better fits their finances and budget. Our mission is to empower as many renters as possible with flexibility over their most significant recurring expense. After deliberately keeping a stealth profile as we built up unprecedented investor support and an enthusiastic user base, we are looking for motivated individuals to help us keep our mission growing. Will you be a part of the team?

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

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

Integrate automated testing 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

Proficient in CI/CD pipeline integration and optimization