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Jun 21, 2026 8 min

How Differential Testing Catches Regressions Without Tests

from Software Testing with Fexingo: QA, Automation, and Reliable Software Engineering Hosted by Fexingo

Episode 65 of Software Testing with Fexingo explores differential testing (a.k.a. metamorphic or diff testing) as a way to catch regressions when no oracle exists. Lucas explains how the technique works by comparing outputs of two program versions on the same input, using real-world examples like JPEG encoders. Luna pushes back on the cost of generating valid inputs and the challenge of flaky diffs. They discuss tools like AFL, LibFuzzer, and Cargo-diff, and when this method beats traditional unit or integration tests. The episode lands on a practical take: use diff testing for core algorithms where a simple transformation (re-encode, re-serialize) should yield identical results. No prior episode has covered this specific technique. #DifferentialTesting #MetamorphicTesting #SoftwareTesting #RegressionTesting #QA #Automation #Fuzzing #LibFuzzer #AFL #CargoDiff #JPEGEncoders #TestOracle #FlakyTests #CoreAlgorithms #TechPodcast #FexingoBusiness #BusinessPodcast #Technology Keep every episode free: buymeacoffee.com/fexingo

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This episode was published on June 21, 2026.

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