Unit Tests Verify Design; Regression Tests Guard Against Past Bugs Returning

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A software development post explains why the same feature can legitimately appear in two separate test files serving distinct purposes. Unit tests are written to confirm a function behaves as designed, using a range of plausible inputs checked against expected outputs. Regression tests, by contrast, are written after a real-world bug occurs, to ensure that specific failure never silently reappears. The article illustrates this with a concrete incident from v1.6.11 development, where an emoji in a build script caused a UnicodeEncodeError on Windows systems using a Japanese locale encoding (cp932). That bug prompted a dedicated two-layer test file that both statically scans scripts for unsafe characters and runs them as subprocesses under cp932 encoding to confirm clean execution.

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OSLabs Releases Open-Source CLI PennyWyze to Audit Claude API Costs

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ProgrammingDEV Community ·

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ProgrammingDEV Community ·

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ProgrammingDEV Community ·

How to Add AI Agent Billing Without Disrupting Its Workflow Loop

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