Why It Matters
Unit tests act as a safety net that lets developers change and improve code with confidence. When a developer modifies a function, the unit tests for that function immediately confirm whether it still works correctly. Without them, every change carries the risk of silently breaking something elsewhere in the system. For your business, unit testing translates to fewer bugs reaching your users, faster development cycles, and lower maintenance costs over time. A well-tested codebase is also easier to hand over to a new team, because the tests document exactly how each piece is supposed to behave.
Example
Your application calculates shipping costs based on weight, destination, and membership tier. A developer writes unit tests covering standard orders, free-shipping thresholds, international surcharges, and edge cases like zero-weight items. Months later, another developer updates the pricing logic to add a new membership tier. The existing unit tests immediately flag that the change accidentally removed the free-shipping threshold for existing tiers, a bug that would have cost you money if it had reached production undetected. Unit testing sits at the foundation of a wider testing approach that includes integration testing, and it is built into how we approach web application development.
