Hi I m stuck trying to nail down the root cause of this issu

Question

Hi I m stuck trying to nail down the root cause of this issue <https github com spring projects spring boot issues 28604> There I wrap a Spring managed bean as a Mockk s spy and inject back to the spring context as a ` Primary` bean a convenient technique to spy on Beans and inject strange behaviors All works good till we hit Spring AOP proxied beans e g ` Cacheable` in my example Some funky interactions are happening there and we end up seeing this exception thread

Mykola Gurov · Answer

```Caused by io mockk MockKException no answer found for TargetSource child of 1 2 getTarget at io mockk impl stub MockKStub defaultAnswer MockKStub kt 93 ~ mockk 1 12 0 jar na at io mockk impl stub MockKStub answer MockKStub kt 42 ~ mockk 1 12 0 jar na at io mockk impl recording states AnsweringState call AnsweringState kt 16 ~ mockk 1 12 0 jar na at io mockk impl recording CommonCallRecorder call CommonCallRecorder kt 53 ~ mockk 1 12 0 jar na at io mockk impl stub MockKStub handleInvocation MockKStub kt 266 ~ mockk 1 12 0 jar na at io mockk impl instantiation JvmMockFactoryHelper$mockHandler$1 invocation JvmMockFactoryHelper kt 23 ~ mockk 1 12 0 jar na at io mockk proxy jvm advice Interceptor call Interceptor kt 21 ~ mockk agent jvm 1 12 0 jar na at io mockk proxy jvm advice BaseAdvice handle BaseAdvice kt 42 ~ mockk agent jvm 1 12 0 jar na at io mockk proxy jvm advice jvm JvmMockKProxyInterceptor interceptNoSuper JvmMockKProxyInterceptor java 45 ~ mockk agent jvm 1 12 0 jar na at org springframework aop TargetSource$Subclass0 getTarget Unknown Source ~ spring aop 5 3 12 jar 5 3 12 ```

Mykola Gurov · Answer

This doesn t look very good to me as I d expect spies to be transparent for non preprogrammed calls but instead I can reproduce the situation with ``` Component class Service Cacheable response cache fun respondCached input String = prefix + + Instant now toEpochMilli Configuration class InjectSpiesConfiguration Bean Primary fun spiedService service Service Service val spyk = spyk service return spyk SpringBootTest class MockkSpykingTest Autowired private val spiedService Service Test fun `hardcoded unwrapping` NB no failures when the following line is commented every spiedService respondCached empty returns val firstUnwrap = spiedService as Advised targetSource target val secondUnwrap = firstUnwrap as Advised targetSource target SoftAssertions assertSoftly it assertThat secondUnwrap isNotInstanceOf Advised class java it assertThat secondUnwrap isInstanceOf Service class java ```

Mykola Gurov · Answer

full code at <https github com mgurov mockk v cached tree mockk slack question>

Mykola Gurov · Answer

Now I understand that wrapping AOP ed bean with spyk is probably not the best of the ideas and we should rather unwrap it first e g `AopTestUtils getUltimateTargetObject service ` but still why does the mock s spy fails that invocation instead of preserving transparent behavior for non intercepted calls

Mattia Tommasone · Answer

thanks for the detailed explanation slightly smiling face this looks pretty nasty indeed my first guess would be that somehow AOP s class decoration is being performed after the one done by mockk s spy so somehow mockk is convinced there is no answer defined for the method you are trying to invoke because it was added later by AOP I don t really know if this is the actual cause nor if there is a way to change the order to make sure mockk always does its magic last and i don t even know if it would be right but it looks like a bug indeed

Mykola Gurov · Answer

reported as <https github com mockk mockk issues 749>