Behavior driven development (BDD) and test driven development (TDD) enable much faster coding when done well in my experience, and that includes full coverage fast unit tests, functional tests, benchmark tests, and integration tests.

Unit tests are worth their weight in gold for quickly finding issues, both in our team's code and especially in cases of subtle changes among language releases, or unanticipated input changes, or dependency changes that are supposed to work but don't.

IMHO unit tests lead to better functional approaches, better long range maintainability, better security, and much better handling of corner cases.