TECH Signal 454
AI migrated legacy COBOL programs to Java, bugs included
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Translating legacy COBOL to Java using AI introduces subtle bugs that are difficult to catch without comprehensive test data. This approach validates agentic coding output deterministically by running source and target code side-by-side off-mainframe to expose edge cases. Engineers can use this to verify that migrated Java code actually matches the original COBOL logic before decommissioning mainframe systems.
Written by elseif from the cluster below · every claim links back to a sourceThe three things worth knowing
The method executes both the COBOL source and generated Java target on commodity hardware using instrumented mocks to perform iterative witness searches.
When the loop reaches a routing boundary, an analyzer identifies a "Locked Paragraph"—a condition preventing deeper exploration—and applies parity-preserving mutations.
Across three case studies, the method pushed branch coverage beyond standard input-search plateaus, reaching 91.90% on an internal production-like program and ensuring the Java matched the COBOL reference in all accepted tests.
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