How a Single Test Case Caught a Million-Dollar Bug

What this episode covers

In this episode, Lucas and Luna unpack a real-world story from a payments startup where one obscure test case — a $0 transaction — exposed a rounding error that would have lost the company over a million dollars annually. They discuss how the bug survived code review, unit tests, and staging, only to be caught by a junior engineer's curiosity during edge-case testing. The conversation covers test psychology, the gap between coverage metrics and actual coverage, and why 'we test everything' is usually a dangerous belief. Lucas argues that most teams over-index on happy-path tests and under-invest in boundary conditions, while Luna shares a story about her own team catching a similar issue in a currency conversion module. They wrap with practical advice: start your testing session with the weirdest input you can think of, not the normal one. This episode is a concrete look at how one test case can save millions and why edge-case testing deserves more respect in engineering culture. #SoftwareEngineering #Testing #EdgeCases #BugStory #Payments #RoundingError #TestCoverage #BoundaryConditions #JuniorEngineer #ProductionBug #QualityAssurance #UnitTests #CodeReview #TechDebt #EngineeringCulture #Technology #FexingoBusiness #BusinessPodcast Keep every episode free: buymeacoffee.com/fexingo

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