Relationship Between Test and Production Code

Exposing private behavior The JUnit tests we write will live in the same project as the production code that they verify. However, we’ll keep the tests separate from the production code within a given project. We’ll be shipping the production code (the target of the tests, sometimes known as the system under test or SUT), but the tests will typically stay behind.

Unit testing is solely a programmer activity. No customers, end-users, or non-programmers will typically see or run our tests.