Test Doubles with Mockito and Spring Test Overrides

Own the decision of what to fake in a test and the mechanics of doing it. A double is legitimate only at a boundary the test cannot reach cheaply; used as a default it deletes the behavior the test was written to prove.

When to use

• Migrating @MockBean and @SpyBean to @MockitoBean and @MockitoSpyBean.
• Deciding whether a dependency should be a mock, a hand-written fake, or the real implementation.
• Stubbing return values, throwing, capturing arguments, or verifying interactions.
• Handling a spy, a final class, a static factory, or a private constructor.
• Fighting UnnecessaryStubbingException, PotentialStubbingProblem, or over-strict verification.
• Reducing a test that mocks the persistence layer or the type under test.

When not to use