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You don't Find Bugs in Legacy Code | David Tanzer

Of course there are defects in legacy code. But when you are a developer working on changing, refactoring or enhancing legacy code, many of the "defects" you'll find are probably desired behaviour (or have been, at some point in time). And even when they are not, you often still cannot be sure if you can fix the undesired behaviour without negatively affecting users. Let me explain...