NullPointerException happens when mock a suspend function B called by another function A

Below code should print 3, but actually it throws below error. Even after I remove all suspend, the print value is 0 instead of 3. It can be reproduced locally even I copy this test to this repo, https://github.com/mockito/mockito-kotlin/blob/main/mockito-kotlin/src/test/kotlin/test/CoroutinesTest.kt

import kotlinx.coroutines.runBlocking
import org.junit.jupiter.api.Test
import org.mockito.kotlin.doReturn
import org.mockito.kotlin.mock

class A{
    suspend fun a():Int{
        return b()
    }
    suspend fun b(): Int{
        return 2
    }
}

class HelloTest {
    @Test
    fun testBWasCalledByA() = runBlocking{
        val a = mock<A>{
            onBlocking { b() } doReturn 3
        }
        val res = a.a()
        println(res)
    }
}

java.lang.NullPointerException: Cannot invoke "java.lang.Number.intValue()"

 

                at org.example.HelloTest$testBWasCalledByA$1.invokeSuspend(HelloTest.kt:24)

                at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)

                at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:56)

                at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:274)

                at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:84)

                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 org.example.HelloTest.testBWasCalledByA(HelloTest.kt:20)

                at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

                at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)

                at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

                at java.base/java.lang.reflect.Method.invoke(Method.java:564)

                at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:389)

                at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:115)

                at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:167)

                at org.junit.jupiter.engine.execution.ThrowableCollector.execute(ThrowableCollector.java:40)

                at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:163)

                at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:110)

                at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:57)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.lambda$execute$3(HierarchicalTestExecutor.java:83)

                at org.junit.platform.engine.support.hierarchical.SingleTestExecutor.executeSafely(SingleTestExecutor.java:66)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:77)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.lambda$null$2(HierarchicalTestExecutor.java:92)

                at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)

                at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:177)

                at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)

                at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)

                at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)

                at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)

                at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)

                at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)

                at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)

                at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:497)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.lambda$execute$3(HierarchicalTestExecutor.java:92)

                at org.junit.platform.engine.support.hierarchical.SingleTestExecutor.executeSafely(SingleTestExecutor.java:66)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:77)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.lambda$null$2(HierarchicalTestExecutor.java:92)

                at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)

                at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:177)

                at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)

                at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)

                at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)

                at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)

                at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)

                at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)

                at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)

                at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:497)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.lambda$execute$3(HierarchicalTestExecutor.java:92)

                at org.junit.platform.engine.support.hierarchical.SingleTestExecutor.executeSafely(SingleTestExecutor.java:66)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:77)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:51)

                at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:43)

                at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:170)

                at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:154)

                at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:90)

                at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:69)

                at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)

                at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)

                at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)

[bohsen]

@Test
fun testBWasCalledByA() = runBlocking{
    val a = mock<A>{
        onBlocking { b() } doReturn 3
    }
    val res = a.a()
    println(res)
}

@ToffeeLu As for the example you’ve provided you invoke an unstubbed function on your mock (this line: val res = a.a()) . Maybe try:

open class A{
    open suspend fun a():Int{
        return b()
    }
    open suspend fun b(): Int{
        return 2
    }
}

class HelloTest {
    @Test
    fun testBWasCalledByA() = runBlocking{
        val a = mock<A>{
            onBlocking { b() } doReturn 3
        }
        val res = a.b() // invoke the stubbed function instead
        println(res)
    }
}

I’ve also added open declarations to your class under test (class A). Not needed if you use inline-mockmaker, AllOpen-plugin or similar.

[ToffeeLu]

Thanks @bohsen , close for now. Will send PR later for the WIKI.