Calling a mock spy that has an AOP advice causes StackOverflow

[LegoRocks]

Explanation

I am currently running into the following problem and I'm a bit lost on how to solve this issue.
I have a basic application with a controller and service. Both are annotated for some AOP functionality. The application itself runs fine and AOP works as expected.

The problem arises during testing, when I want to mock my service bean to spy and verify its usage. This causes an StackOverflowError, I guess because the mock and AOP interceptor keep calling each other?

Stacktrace

java.lang.StackOverflowError: null
	at java.base/java.lang.ref.Reference.refersToImpl(Reference.java:384)
	at java.base/java.lang.ref.Reference.refersTo(Reference.java:375)
	at java.base/java.lang.ThreadLocal$ThreadLocalMap.set(ThreadLocal.java:552)
	at java.base/java.lang.ThreadLocal.set(ThreadLocal.java:265)
	at java.base/java.lang.ThreadLocal.set(ThreadLocal.java:251)
	at io.mockk.proxy.jvm.advice.SelfCallEliminatorCallable.call(SelfCallEliminatorCallable.kt:20)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper.handleOriginalCall(JvmMockFactoryHelper.kt:96)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper.access$handleOriginalCall(JvmMockFactoryHelper.kt:19)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper$mockHandler$1$invocation$1$1.invoke(JvmMockFactoryHelper.kt:28)
	at io.mockk.impl.stub.MockKStub$handleInvocation$originalPlusToString$1.invoke(MockKStub.kt:235)
	at io.mockk.impl.stub.SpyKStub.defaultAnswer(SpyKStub.kt:15)
	at io.mockk.impl.stub.MockKStub.answer(MockKStub.kt:44)
	at io.mockk.impl.recording.states.AnsweringState.call(AnsweringState.kt:16)
	at io.mockk.impl.recording.CommonCallRecorder.call(CommonCallRecorder.kt:53)
	at io.mockk.impl.stub.MockKStub.handleInvocation(MockKStub.kt:271)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper$mockHandler$1.invocation(JvmMockFactoryHelper.kt:24)
	at io.mockk.proxy.jvm.advice.Interceptor.call(Interceptor.kt:21)
	at com.example.$DemoServiceImpl$Definition$Intercepted.$$access$$getDemo(Unknown Source)
	at com.example.$DemoServiceImpl$Definition$Exec.dispatch(Unknown Source)
	at io.micronaut.context.AbstractExecutableMethodsDefinition$DispatchedExecutableMethod.invoke(AbstractExecutableMethodsDefinition.java:456)
	at io.micronaut.aop.chain.MethodInterceptorChain.proceed(MethodInterceptorChain.java:134)
	at com.example.$DemoServiceImpl$Definition$Intercepted.getDemo(Unknown Source)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at io.mockk.proxy.jvm.advice.MethodCall.call(MethodCall.kt:14)
	at io.mockk.proxy.jvm.advice.SelfCallEliminatorCallable.call(SelfCallEliminatorCallable.kt:14)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper.handleOriginalCall(JvmMockFactoryHelper.kt:96)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper.access$handleOriginalCall(JvmMockFactoryHelper.kt:19)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper$mockHandler$1$invocation$1$1.invoke(JvmMockFactoryHelper.kt:28)
	at io.mockk.impl.stub.MockKStub$handleInvocation$originalPlusToString$1.invoke(MockKStub.kt:235)
	at io.mockk.impl.stub.SpyKStub.defaultAnswer(SpyKStub.kt:15)
	at io.mockk.impl.stub.MockKStub.answer(MockKStub.kt:44)
	at io.mockk.impl.recording.states.AnsweringState.call(AnsweringState.kt:16)
	at io.mockk.impl.recording.CommonCallRecorder.call(CommonCallRecorder.kt:53)
	at io.mockk.impl.stub.MockKStub.handleInvocation(MockKStub.kt:271)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper$mockHandler$1.invocation(JvmMockFactoryHelper.kt:24)
	at io.mockk.proxy.jvm.advice.Interceptor.call(Interceptor.kt:21)
	at com.example.DemoServiceImpl.getDemo(DemoServiceImpl.kt:9)
	at com.example.$DemoServiceImpl$Definition$Intercepted.$$access$$getDemo(Unknown Source)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at io.mockk.proxy.jvm.advice.MethodCall.call(MethodCall.kt:14)

Minimal example

Environment info

• Micronaut: 4.6.3
• Java: 21
• Language: Kotlin
• Testframework: Kotest

AOP Annotation

@Inherited
@InterceptorBinding
@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.CLASS)
annotation class DemoAdvice

Controller

@DemoAdvice
@Controller("/demo")
open class DemoController(private val demoService: DemoService) {

    @Get("/{id}")
    open fun get(id: Long) = demoService.getDemo(id)
}

Service

interface DemoService {

    fun getDemo(id: Long): Long
}

@DemoAdvice
@Singleton
open class DemoServiceImpl : DemoService {

    override fun getDemo(id: Long) = id
}

Test

@MicronautTest
class DemoControllerTest(
    private val demoService: DemoService,
    @Client("/") private val httpClient: HttpClient,
    private val applicationContext: ApplicationContext,
) : ShouldSpec({

    should("run without problems") {
        val mock = getMock(demoService)

        val getRequest = HttpRequest.GET<Any>("/demo/1")
        shouldNotThrowAny { httpClient.toBlocking().retrieve(getRequest) }
        verify(exactly = 1) { mock.getDemo(1) }
    }

}) {

    @MockBean(DemoService::class)
    fun demoService(): DemoService = spyk(applicationContext.getBean(DemoServiceImpl::class.java))
}

Workarounds

I found a couple of workarounds but I'd like to understand the problem first, as all these would require some major refactoring of my existing code base and aren't applicable for all cases.

@MockBean(DemoService::class)
    fun demoService(): DemoService = spyk(DemoServiceImpl())

I can create the service class manually instead of getting it from the application context. But is also requires to inject all the dependencies for the service manually.

@MockBean(DemoService::class)
    fun demoService(): DemoService = spyk(mockk<DemoService>())

I can fully mockk the service. Requires writing a lot of additional code for mock behavior. Alternatively it also works if the mock delegates all calls to an injected DemoService bean.

I'll appreciate any ideas, feeback or workarounds.