NPE when trying to access firstArg() and args[0] on mocked extension function

[spyro2000]

Prerequisites

Please answer the following questions for yourself before submitting an issue.

• I am running the latest version (1.12.4)
• I checked the documentation and found no answer
• I checked to make sure that this issue has not already been filed

Expected Behavior

args[0] and firstArg<String>() should deliver correct value as non-nullable String

Current Behavior

Nullpointer Exceptions when accessing first param in mocked answer of extension method (with mockkStatic). For some reason, index 1 provides the value (instead of index 0 as expected).

Failure Information (for bugs)

For some reason, the parameters seems to be offset by one.

Steps to Reproduce

Please provide detailed steps for reproducing the issue.

Given this extension method of Spring Data:

fun <T, ID> CrudRepository<T, ID>.findByIdOrNull(id: ID): T? = findById(id).orElse(null)

... and following code to mock a call like repo.findByIdOrNull("myId") in a test:

 mockkStatic("org.springframework.data.repository.CrudRepositoryExtensionsKt")
  every { repo.findByIdOrNull(any()) } answers { // SINGLE ARGUMENT
            val arg1 = arg<String>(1) // works (value = "myId")
            val arg0 = arg<String>(0) // fails (NPE)
            val firstArg = firstArg<String>() // failes (NPE)
 }

Context

Please provide any relevant information about your setup. This is important in case the issue is not reproducible except for under certain conditions.

• MockK version: 1.12.4
• OS: Win10-x64 Pro
• Kotlin version: 1.6.20
• JDK version: 17
• JUnit version: 5
• Spring Boot 2.6.7
• Type of test: unit test

Failure Logs

Please include any relevant log snippets or files here.

Stack trace

// -----------------------[ YOUR STACK STARTS HERE ] -----------------------
class com.xxx.xxx.xxxapi.xxxconfig.IxxxConfigRepo$Subclass0 cannot be cast to class java.lang.String (com.xxx.xxx.xxxapi.xxxconfig.IxxxConfigRepo$Subclass0 is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstrap')
java.lang.ClassCastException: class com.xxx.xxx.xxxapi.xxxconfig.IxxxConfigRepo$Subclass0 cannot be cast to class java.lang.String (com.xxx.xxx.xxxapi.xxxconfig.IxxxConfigRepo$Subclass0 is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstrap')
	at com.xxx.xxx.xxxapi.xxxconfig.domain.services.xxxConfigServiceTest$setup$7.invoke(xxxConfigServiceTest.kt:126)
	at com.xxx.xxx.xxxapi.xxxconfig.domain.services.xxxConfigServiceTest$setup$7.invoke(xxxConfigServiceTest.kt:42)
	at io.mockk.MockKStubScope$answers$1.invoke(API.kt:2117)
	at io.mockk.MockKStubScope$answers$1.invoke(API.kt:2091)
	at io.mockk.FunctionAnswer.answer(Answers.kt:19)
	at io.mockk.impl.stub.AnswerAnsweringOpportunity.answer(AnswerAnsweringOpportunity.kt:14)
	at io.mockk.impl.stub.MockKStub.answer(MockKStub.kt:54)
	at io.mockk.impl.recording.states.AnsweringState.call(AnsweringState.kt:16)
	at io.mockk.impl.recording.CommonCallRecorder.call(CommonCallRecorder.kt:53)
	at io.mockk.impl.stub.MockKStub.handleInvocation(MockKStub.kt:266)
	at io.mockk.impl.instantiation.JvmMockFactoryHelper$mockHandler$1.invocation(JvmMockFactoryHelper.kt:23)
	at io.mockk.proxy.jvm.advice.Interceptor.call(Interceptor.kt:21)
	at org.springframework.data.repository.CrudRepositoryExtensionsKt.findByIdOrNull(CrudRepositoryExtensions.kt:26)
	at com.xxx.xxx.xxxapi.xxxconfig.domain.services.xxxConfigService.findById(xxxConfigService.kt:49)
	at com.xxx.xxx.xxxapi.xxxconfig.domain.services.xxxConfigServiceTest.findById(xxxConfigServiceTest.kt:65)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:567)
	at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:725)
	at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
	at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
	at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
	at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
	at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$7(TestMethodTestDescriptor.java:214)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:210)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:66)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:151)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1507)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1507)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.processAllTestClasses(JUnitPlatformTestClassProcessor.java:99)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.access$000(JUnitPlatformTestClassProcessor.java:79)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.stop(JUnitPlatformTestClassProcessor.java:75)
	at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:61)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:567)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
	at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
	at com.sun.proxy.$Proxy2.stop(Unknown Source)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker$3.run(TestWorker.java:193)
	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 worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
	at worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)


// -----------------------[ YOUR STACK TRACE ENDS HERE ] -----------------------

Minimal reproducible code (the gist of this issue)

// -----------------------[ GRADLE DEFINITIONS ] -----------------------
dependencies {
    // kotlin essentials
    implementation("org.jetbrains.kotlin:kotlin-reflect")
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core")

    // Spring Boot stuff
    implementation("org.springframework.boot:spring-boot-starter-web")
    implementation("org.springframework.boot:spring-boot-starter-validation")
    implementation("org.springframework.boot:spring-boot-starter-actuator")
    developmentOnly("org.springframework.boot:spring-boot-devtools")
 
    // Testing
    testImplementation("org.springframework.boot:spring-boot-starter-test") {
        exclude(module = "mockito-core") // We use mockK instead (see below)
    }
    testImplementation("io.mockk:mockk:1.12.4")
    testImplementation("org.assertj:assertj-core:3.20.2") // Temp. workaround for https://github.com/assertj/assertj-core/issues/2357
    testImplementation("com.ninja-squad:springmockk:3.1.1") // for spring-based unit/integration tests
  
}
// -----------------------[ YOUR CODE STARTS HERE ] -----------------------
// See above
// -----------------------[ YOUR CODE ENDS HERE ] -----------------------

[aSemy]

I get the same with MockK 1.12.5. When I put a breakpoint in the answers { } block and try and run firstArg<>(), I get this exception

org.jetbrains.kotlin.backend.common.BackendException : Backend Internal error: Exception during file facade code generation
File being compiled: mock:///fragment.kt
The root cause java.lang.NullPointerException was thrown at: org.jetbrains.kotlin.codegen.ExpressionCodegen.generateExtensionReceiver(ExpressionCodegen.java:3123)

If I try and manually get the first arg, it seems to work

val firstArg = it.invocation.args[0] as MyClass
println(firstArg) // prints the expected result

But when I run the test, it fails.

UPDATE: this is a value class issue. It might be fixed by #872.

In my instance the function I was stubbing returned a sealed interface, and one of the implementations is a @JvmInline value class.

sealed interface Evaluation {
  object Pass: Evaluation

  @JvmInline
  value class Fail(val message: String): Evaluation
}

every {
    myService.evaluate(
        data = any<MyClass>(),
    )
} answers {
  val dataArg = firstArg<MyClass>()
  if (dataArg == <something>) {
    Evaluation.Pass
  } else {
    Evaluation.Fail("some message")
  }
}

The workaround is to turn the value class into a data class. This isn't ideal, but it works.

  data class Fail(val message: String): Evaluation

[stale]

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