Using the result of callOriginal() inside coAnswers throws a fatal exception when the original contains a call to delay

[saibotma]

Expected Behavior

No exception gets thrown and the result of callOriginal() can be used.

Current Behavior

An exception gets thrown.

Failure Information (for bugs)

It works, when wrapping callOriginal() inside a suspending function:

import io.mockk.coEvery
import io.mockk.mockk
import kotlinx.coroutines.delay
import kotlinx.coroutines.runBlocking

class ClassToMock() {
    suspend fun methodToMock(): Int {
        delay(1000)
        return 1
    }
}

fun main(): Unit = runBlocking {
    val mocked = mockk<ClassToMock> {
        coEvery { methodToMock() } coAnswers {
            suspend fun test(): Int = callOriginal()
            test() + 1
        }
    }

    val result = mocked.methodToMock()
    println(result)
}

It also works when removing the call to delay.

Steps to Reproduce

Run the example code.

Context

• MockK version: 1.13.9
• OS: MacOS Sonoma 14.1.1
• Kotlin version: 1.9.22
• JDK version: OpenJDK 17.0.6

Failure Logs

Stack trace

Exception in thread "main" kotlinx.coroutines.CoroutinesInternalError: Fatal exception in coroutines machinery for CancellableContinuation(DispatchedContinuation[BlockingEventLoop@3f81621c, Continuation at ClassToMock.methodToMock(main.kt:8)@7c2924d7]){Cancelled}@40fa8766. Please read KDoc to 'handleFatalException' method and report this incident to maintainers
	at kotlinx.coroutines.DispatchedTask.handleFatalException(DispatchedTask.kt:144)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:115)
	at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:280)
	at kotlinx.coroutines.EventLoopImplBase.shutdown(EventLoop.common.kt:225)
	at kotlinx.coroutines.EventLoop.decrementUseCount(EventLoop.common.kt:113)
	at kotlinx.coroutines.EventLoop.decrementUseCount$default(EventLoop.common.kt:107)
	at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:91)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:59)
	at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:38)
	at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)
	at MainKt.main(main.kt:13)
	at MainKt.main(main.kt)
	Suppressed: kotlinx.coroutines.internal.DiagnosticCoroutineContextException: [BlockingCoroutine{Cancelled}@7eb200ce, BlockingEventLoop@3f81621c]
Caused by: java.lang.ClassCastException: class kotlin.coroutines.jvm.internal.CompletedContinuation cannot be cast to class kotlinx.coroutines.internal.DispatchedContinuation (kotlin.coroutines.jvm.internal.CompletedContinuation and kotlinx.coroutines.internal.DispatchedContinuation are in unnamed module of loader 'app')
	at kotlinx.coroutines.CoroutineDispatcher.releaseInterceptedContinuation(CoroutineDispatcher.kt:166)
	at kotlin.coroutines.jvm.internal.ContinuationImpl.releaseIntercepted(ContinuationImpl.kt:118)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:39)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:104)
	... 11 more
Exception in thread "main" java.lang.ClassCastException: class kotlin.coroutines.intrinsics.CoroutineSingletons cannot be cast to class java.lang.Number (kotlin.coroutines.intrinsics.CoroutineSingletons is in unnamed module of loader 'app'; java.lang.Number is in module java.base of loader 'bootstrap')
	at MainKt$main$1$mocked$1$2.invokeSuspend(main.kt:16)
	at MainKt$main$1$mocked$1$2.invoke(main.kt)
	at MainKt$main$1$mocked$1$2.invoke(main.kt)
	at io.mockk.MockKStubScope$coAnswers$1.invokeSuspend(API.kt:2259)
	at io.mockk.MockKStubScope$coAnswers$1.invoke(API.kt)
	at io.mockk.MockKStubScope$coAnswers$1.invoke(API.kt)
	at io.mockk.CoFunctionAnswer$answer$1.invokeSuspend(Answers.kt:33)
	at io.mockk.CoFunctionAnswer$answer$1.invoke(Answers.kt)
	at io.mockk.CoFunctionAnswer$answer$1.invoke(Answers.kt)
	at io.mockk.JvmCoroutineCall.callCoroutine(InternalPlatformDsl.kt:236)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at io.mockk.JvmCoroutineCall.callWithContinuation(InternalPlatformDsl.kt:241)
	at io.mockk.CoFunctionAnswer.answer(Answers.kt:34)
	at io.mockk.impl.stub.AnswerAnsweringOpportunity.answer(AnswerAnsweringOpportunity.kt:14)
	at io.mockk.impl.stub.MockKStub.answer(MockKStub.kt:54)
	at io.mockk.impl.recording.states.AnsweringState.call(AnsweringState.kt:16)
	at io.mockk.impl.recording.CommonCallRecorder.call(CommonCallRecorder.kt:53)
	at io.mockk.impl.stub.MockKStub.handleInvocation(MockKStub.kt:269)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper$mockHandler$1.invocation(JvmMockFactoryHelper.kt:24)
	at io.mockk.proxy.jvm.advice.Interceptor.call(Interceptor.kt:21)
	at ClassToMock.methodToMock(main.kt:7)
	at MainKt$main$1.invokeSuspend(main.kt:20)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
	at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:280)
	at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:85)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:59)
	at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:38)
	at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)
	at MainKt.main(main.kt:13)
	at MainKt.main(main.kt)

Minimal reproducible code (the gist of this issue)

import io.mockk.coEvery
import io.mockk.mockk
import kotlinx.coroutines.delay
import kotlinx.coroutines.runBlocking

class ClassToMock() {
    suspend fun methodToMock(): Int {
        delay(1000)
        return 1
    }
}

fun main(): Unit = runBlocking {
    val mocked = mockk<ClassToMock> {
        coEvery { methodToMock() } coAnswers {
            callOriginal() + 1
        }
    }

    val result = mocked.methodToMock()
    println(result)
}