What is @SpringBootTest, and when should you use it? | Interview Question

Reaching for @SpringBootTest for every single test class — including ones that only need to test one service's logic in isolation — needlessly slows down the entire test suite, since each unique context configuration Spring caches and reuses only if subsequent tests request an identical context; slight configuration differences between test classes silently force expensive context re-creation. Narrower slice tests (@WebMvcTest, @DataJpaTest) or plain unit tests with Mockito are usually the better default.

Overusing @SpringBootTest Is the Most Common Spring Testing Mistake