Regression testing is when you re-test everything in your suite to see if it still does the same thing it originally did (correctly).
Sanity testing is the bare minimum testing that validates your core product to ensure it can do the most primal functions necessary to survive.
Coverage looks at how far your testing extends – does it extend to everything you need it to reach?
Leadership is knowing where, when, and how you need each one but more importantly, knowing when to pump the brakes when you are about to ship your final product.
