Code review

Code review is another developer reading a change before it is merged, checking that it does what it claims, handles the awkward cases, and fits the conventions of the codebase.

It catches defects, but its larger effect is on the team: knowledge of every part of the system reaches more than one person, standards are applied consistently, and nobody becomes the only individual who understands a critical component. That is a continuity benefit as much as a quality one.

It works when changes are small and reviews are prompt. A four-thousand-line change receives approval rather than review, and a review that arrives two days later has already cost more in waiting than it saves in defects.