Double-entry bookkeeping revolutionised business by introducing a self-checking system of financial integrity. In the world of software, Behaviour-Driven Development (BDD) does something strikingly similar — pairing each feature with a clear, testable description of how it should behave. Double-entry bookkeeping and automated software testing might seem worlds apart – one emerged in Renaissance-era accounting and the other in modern software development. Yet conceptually, they serve a similar purpose: both introduce systems of checks and balances to ensure integrity and accuracy in their respective domains. In accounting, double-entry bookkeeping requires every transaction to be recorded in two accounts (debits and credits) that must balance, creating an internal self-checking mechanism. In software, automated tests act as a parallel record of expected behaviour, continuously verifying that the code produces the intended outcomes. This post explores how a 500-year-old accounting innovation revolutionised financial record-keeping and how its spirit lives on in the way we write and test software today.

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