Top Mockito priorities (equal importance):

I. Maximize test's clarity
II. Maximize test's failure output (easy test failure debugging)
III. Guide the engineer toward cleaner, higher quality tests that are easy to maintain

Use cases, in the order of importance.

1. Unused stubbing is dead code, an irrelevant detail that clutters test's clarity.
2. Unintentionally unused stubbing can make test failures harder to debug.
3. When the stubbed call needs to be verified, it is declared twice in test (violation of DRY principle).

Proposed solution

The solution consists of multiple changes. Perhaps it's better to show the code first, then describe the changes.

//JUnit rule automatically fails when stubs are unused:
MockitoJUnit.rule().strict();
//Offer a way to make specific stubbings optional:
given(mock.foo(), optional()).willReturn("bar");
//Offer a way to validate stubs for users who don't use JUnit rules:
Mockito.validateStubs();

Summary:

1. All stubbed method calls must be used (realized), otherwise the test fails.
2. Test failure is triggered by JUnit rule or Runner

• When JUnit rule or runner is not used, new Mockito.verifyStubs() method can be used. The method is not intended for engineers to use in tests. It's intended for framework integrators (TestNG runners) or a common base class.

4. "optional" stubbings. Consider default stubbings that user may put in test constructor or setup method. Those default stubbings are used by most test methods but not all. This is a legit scenario that needs to be supported.
5. verifyNoMoreInteractions() no longer includes used stubs for validation when strict rule / runner is in use.

Mockito 3:

1. Strict rule by default
2. verifyNoMoreInteractions() no longer includes used stubs for validation