Bug: cannot capture nullable argument in mocked suspending methods

[rocca23]

Example code:

@Test
    fun foo() {
        val arg = mutableListOf<String?>()
        val server = mockk<Server> {
            coEvery { foo(captureNullable(arg)) } just runs
        }
        runBlocking {
            server.foo()
        }
        assertNull(arg.last())
    }

Gist with full code

Executing the test produces this exception:

io.mockk.MockKException: no answer found for: Server(#1).foo(null, continuation {})
at io.mockk.impl.stub.MockKStub.defaultAnswer(MockKStub.kt:90)
at io.mockk.impl.stub.MockKStub.answer(MockKStub.kt:42)
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:263)
at io.mockk.impl.instantiation.JvmMockFactoryHelper$mockHandler$1.invocation(JvmMockFactoryHelper.kt:25)
at io.mockk.proxy.jvm.advice.Interceptor.call(Interceptor.kt:20)
at io.mockk.proxy.jvm.advice.BaseAdvice.handle(BaseAdvice.kt:42)
at io.mockk.proxy.jvm.advice.jvm.JvmMockKProxyInterceptor.interceptNoSuper(JvmMockKProxyInterceptor.java:45)
at com.app.test.Server$Subclass0.foo(Unknown Source)
at com.app.test.Server$DefaultImpls.foo$default(UnitTests.kt:43)
at com.app.test.UnitTests$foo$1.invokeSuspend(UnitTests.kt:35)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
...

Replacing captureNullable(arg) with any(), or making arg not-null and using capture(arg), both don't produce the error.

Context

• MockK version: 1.9.3
• Kotlin version: 1.3.50 (coroutines 1.3.1)
• JUnit version: 4
• Type of test: both in Instrumented test (Android 9) and Unit test (JRE: 1.8.0_202-release-1483-b49-5587405 amd64; JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o; Linux 5.0.0-27-generic).

[rocca23]

Must be similar to the recent #353 . Also, I was trying to work this around by using verify and withNullableArg, but the latter is broken with null values as per #323 .
At the moment it looks like it's impossible to verify null arguments in tests.

[nathanmalloch]

sadly this is still an issue. is there a work around for this for now?

[michaelliangbrex]

Is the issue fixed?

[whck6]

+1