Honey, where are my tests?
Having identified a number of different types of tests, you can already imagine that each tests has its own place in the process.
The process here is key: because software development is complex and consists of several steps, it just makes sense to validate each of these steps. We'll outline a lineair process, but of course in practice there's more iteration between steps. That's fine and is in fact where tests offer the confidence of moving back and forth!