Cannot mock function returning nullable value class

[TimonKanters-TomTom]

Expected Behavior

Being able to mock functions returning nullable value classes.

Current Behavior

It's possible to mock functions returning value classes, but only if they return a non-null value. Otherwise an exception is thrown while trying to execute the every statement.

Failure Information (for bugs)

Steps to Reproduce

Create a class with a function that returns a nullable value class (e.g., fun getInstance(): TestValueClass?) and try to mock its getInstance() call.

Note that fun getInstance(): TestValueClass (without ?) can be mocked successfully.

Context

• MockK version: 1.12.3
• OS: Windows 10
• Kotlin version: 1.6.10
• JDK version: 1.8
• JUnit version:4.13.2
• Type of test: unit test

Stack trace

io.mockk.MockKException: Class cast exception happened.
Probably type information was erased.
In this case use `hint` before call to specify exact return type of a method.

io.mockk.MockKException: Class cast exception happened.
Probably type information was erased.
In this case use `hint` before call to specify exact return type of a method.

	at app//io.mockk.impl.InternalPlatform.prettifyRecordingException(InternalPlatform.kt:74)
	at app//io.mockk.impl.eval.RecordedBlockEvaluator.record(RecordedBlockEvaluator.kt:66)
	at app//io.mockk.impl.eval.EveryBlockEvaluator.every(EveryBlockEvaluator.kt:30)
	at app//io.mockk.MockKDsl.internalEvery(API.kt:93)
	at app//io.mockk.MockKKt.every(MockK.kt:98)
	at app//<omitted>.ValueClassMockKTest.return nullable value class from mockk(ValueClassMockKTest.kt:98)
	at java.base@11.0.2/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base@11.0.2/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base@11.0.2/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base@11.0.2/java.lang.reflect.Method.invoke(Method.java:566)
	at app//org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at app//org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at app//org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
	at app//org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at app//org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at app//org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at app//org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at app//org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at app//org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at app//org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at app//org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at app//org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at app//org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at app//org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at app//org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at app//org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.runTestClass(JUnitTestClassExecutor.java:110)
	at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:58)
	at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:38)
	at org.gradle.api.internal.tasks.testing.junit.AbstractJUnitTestClassProcessor.processTestClass(AbstractJUnitTestClassProcessor.java:62)
	at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:51)
	at java.base@11.0.2/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base@11.0.2/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base@11.0.2/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base@11.0.2/java.lang.reflect.Method.invoke(Method.java:566)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
	at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
	at com.sun.proxy.$Proxy5.processTestClass(Unknown Source)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker$2.run(TestWorker.java:176)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.executeAndMaintainThreadName(TestWorker.java:129)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:100)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:60)
	at org.gradle.process.internal.worker.child.ActionExecutionWorker.execute(ActionExecutionWorker.java:56)
	at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:133)
	at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:71)
	at app//worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
	at app//worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)
Caused by: java.lang.ClassCastException: class java.lang.Integer cannot be cast to class <omitted>.ValueClassMockKTest$TestValueClass (java.lang.Integer is in module java.base of loader 'bootstrap'; <omitted>.ValueClassMockKTest$TestValueClass is in unnamed module of loader 'app')
	at <omitted>.ValueClassMockKTest$TestClass.getInstance-S9MxRGs(ValueClassMockKTest.kt:92)
	at <omitted>.ValueClassMockKTest$return nullable value class from mockk$mock$1$1.invoke-M5bYiII(ValueClassMockKTest.kt:98)
	at <omitted>.ValueClassMockKTest$return nullable value class from mockk$mock$1$1.invoke(ValueClassMockKTest.kt:98)
	at io.mockk.impl.eval.RecordedBlockEvaluator$record$block$1.invoke(RecordedBlockEvaluator.kt:25)
	at io.mockk.impl.eval.RecordedBlockEvaluator$enhanceWithRethrow$1.invoke(RecordedBlockEvaluator.kt:78)
	at io.mockk.impl.recording.JvmAutoHinter.autoHint(JvmAutoHinter.kt:23)
	at io.mockk.impl.eval.RecordedBlockEvaluator.record(RecordedBlockEvaluator.kt:40)
	... 47 more

Minimal reproducible code (the gist of this issue)

    @JvmInline
    value class TestValueClass(private val value: Int)

    class TestClass {
        fun getInstance(): TestValueClass? = error("Must be mocked")
    }

    @Test
    fun `return nullable value class from mockk`() {
        val mock = mockk<TestClass> {
            every { getInstance() } returns TestValueClass(1)
        }

        assertEquals(valueClassInstance, mock.getInstance())
    }

Sidenote

I realise that #152 also discussed value classes, but as part of that issue it seems main support has been added. (Thank you for that.) As such this seemed more like a separate issue and worth a dedicated bug report. Feel free to merge if this should be part of that issue instead.

[mdekaste]

Bump for visibility, especially now that duration has been released officially in 1.6, the usage of nullable value classes will grow.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. If you are sure that this issue is important and should not be marked as stale just ask to put an important label.

[TimonKanters-TomTom]

This is an important issue to make effective use of value classes. @oleksiyp / @Raibaz would you be able to label this as important?

[NemanjaBozovic-TomTom]

Hey, any update on the issue?

[ghackett]

Seems like this issue now applies for non-nullable value classes as of 1.13.10

interface DurationProvider {
  val myDuration: Duration
}

val mockProvider = mockk<DurationProvider> {
  every { myDuration } returns 5.minutes
}

runTest {
  delay(mockProvider.myDuration) // works fine on 1.13.9, class cast exception on 1.13.10
}