Essential Testing: testing the right things, at the right time, to the right level of detail, in the most efficient manner, to prove a software system works and works correctly.

The type of testing we do and what we test to prove that a system works depends on who we are proving the system to: the stakeholders. We do the proving, they assess the proof, and provide the approval. They help us determine the right things to test, the level of test detail, and the proper timing of the tests.