Sample answer is:
We follow Test Driven Development (TDD) approach. In this approach we first write unit tests to fail the code. Then we write code to implement a feature. We try to write a large number of Unit tests that can be run in parallel. It saves time during build.
We also write Unit test that are independent of the time and environment where they are run. The unit tests are the plugged into the build process. Therefore, we can catch any issues in code early.
Whenever we have to create new feature on existing code. We first write some tests that can fail with the new feature. Then we write the feature in such a way that the tests start passing. It gives us confidence in releasing the code to production.