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Senior Software Development Engineer in Test (SDET)

New York, New York, United States; San Francisco, California, United States

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 2025 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
  • 4+ 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
  • Skilled in test strategy development, risk analysis, and test architecture
  • Advanced debugging, troubleshooting, and root cause analysis
  • Solid understanding of database systems and advanced SQL
  • Experience with observability and monitoring tools (e.g., DataDog, NewRelic)
  • Excellent cross-functional communication and mentorship skills
  • Strong written and verbal communication skills; able to collaborate across functions


This is a hybrid position with on-site expectations of 3 days per week in our New York City Headquarters (Union Square) or Bay Area (San Mateo). For candidates outside of these areas, you may be eligible for our relocation assistance program.

The compensation range for this role will be commensurate with the candidate's experience and Flex's internal leveling guidelines and benchmarks. 

  • For working locations in NY/NJ/CA, the base salary pay range will be $158,000-$172,000.

Life at Flex:

We understand that it takes a diverse team of highly intelligent, curious, determined, empathetic, and self aware people to grow a successful company. Our HQ is located in New York City, but we have employees located throughout the US, Australia, Canada and South America. We are growing quickly, but deliberately, with a focus on building an inclusive culture. Our dynamic team has incredible perspectives to share, just as we know you do, and we take great pride in being an equal opportunity workplace.

We offer many employee benefits. For full time, U.S. based employees we offer:

  • Competitive pay
  • 100% company-paid medical, dental, and vision
  • 401(k) + company equity
  • Unlimited paid time off + 13 company paid holidays
  • Parental leave 
  • Flex Cares Program: Non-profit company match + pet adoption coverage
  • Free Flex subscription

 For full time non-US employees, we offer

  • Competitive Pay
  • Company Equity
  • Unlimited PTO

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