Тестируемый класс -
@Service
class SomeService @Autowired constructor(
    @Value("\${app.value}") private var configValue: String,
    private val someClass: SomeClass
) {

Бин -

@Configuration
open class BeanConfig @Autowired constructor(
    @Value("\${value:NONE}") private var value: String
) {

    @Bean
    open fun someClass(): SomeClass {
        return SomeClass(value)
    }
}
Тест -
class SomeServiceTest : BaseServiceTest() {

    @Mock
    var someClass: SomeClass = Mockito.mock(SomeClass::class.java)

    @InjectMocks
    lateinit var someService: SomeService
}

BaseTest -
@SpringBootTest
@ExtendWith(SpringExtension::class)
@TestPropertySource("classpath:application-test.properties")
open class BaseServiceTest {

    @MockBean
    lateinit var someComponent: SomeComponent

}