The developer first writes an (initially failing) automated test case that specifies the desired change or new feature, then generates the minimum amount of code to pass the test, and finally transforms the new code to acceptable standards. A common approach to evidencing the use of TDD is ' code coverage.
While high coverage does not provide sufficient use of TDD, coverage below 80% is likely to suggest flaws in a team's TDD mastery. Version control logs suggest that the test code is reviewed in approximately comparable quantities. The time the product code is checked.