Legacy Monolith Test Suite Modernization & Anti-Pattern Refactoring

Senior Automation Engineer · Year 1 · Q4 (Previous SaaS)

Quality & AutomationYear 1 · Q4 (Previous SaaS)

Led the architectural overhaul of a 5,000+ legacy test suite, replacing tightly-coupled database integration dependencies with mocking interfaces to reduce build execution times by 65%.

⚡65% Reduction in Build Execution Time
⚡Flakiness Rate Dropped from 18% to <0.5%
⚡5,000+ Legacy Tests Refactored
JavaJUnit 4MockitoJenkinsSonarQube

Situation

The 8-year-old core SaaS monolith contained over 5,000 integration tests written without strict layering. Over 40% of tests performed full database mutations and heavy file I/O operations to validate simple business logic rules, leading to an unsustainable 18% global flakiness rate and continuous pipeline blockages.

Task

Decompose and refactor the legacy test suite into a strict testing pyramid, decoupling unit logic from external database dependencies while establishing automated code quality gates in CI.

Action

  • Automated Flakiness Quarantining: Built a custom JUnit listener that auto-detected tests failing more than once in 10 runs, automatically annotating them with @Flaky and quarantining them out of PR-blocking pipelines into a non-blocking diagnostic queue.
  • Service-Layer Mocking Modernization: Replaced direct database calls in core domain verification tests with isolated Mockito context mocks, decoupling business logic checks from underlying relational schemas.
  • Static Analysis Quality Gates: Configured SonarQube rules inside Jenkins to fail builds if a new PR introduced thread-unsafe static variables or direct Thread.sleep() calls inside test methods.

Result

  • Dropped global pipeline flakiness from 18% to under 0.5%.
  • Reduced total build execution time from 90 minutes to 31 minutes, saving hundreds of monthly developer waiting hours.