Mock throwing of Exception with Android Coroutines

Question

I am introducing coroutines to an android app I am working. There is lots of legacy but I am now adding some new networking code and using coroutines for it.

EDIT Updating to add the whole test

coEvery { service.getAddress(any(), any(), any()) } coAnswers { throw Exception("Test Exception") }
val subject = repository.getAddress(123, "en", null)

coVerify(exactly = 1) { service.getAddress(any(), any(), any())}

So the line coEvery { service.getAddress(any(), any(), any()) } coAnswers { throw Exception("Test Exception") } in the test on it's own doesn't cause an issue. It falls down when adding val subject = repository.getAddress(123, "en", null)

EDIT 2 TO INCLUDE REPO Here is the repo:

class AddressRepository (
    val addressRestService: AddressRestService,
    val dispatcher: CoroutineDispatcher
){
    suspend fun getAddress(
        wlid: Int,
        locale: String?,
        googleAddressObject: GeoResponse?
    ) : AddressForm = withContext(dispatcher) {
             addressRestService.getAddress(wlid, locale, googleAddressObject)
    }
}

I am using clean architecture and I am trying to test my repository. I am using the Mockk lib and I am trying to test a failure.

Below is a snippet:

coEvery {
    service.getAddress(123, "en", null)
} throw Exception()

When running the above I get test failure with the following stack trace:

java.lang.Exception
    at **.*******.data.repository.AddressRepositoryTest$when getAddress is called, returns false$1.invokeSuspend(AddressRepositoryTest.kt:52)
    at **.*******.data.repository.AddressRepositoryTest$when getAddress is called, returns false$1.invoke(AddressRepositoryTest.kt)
    at kotlinx.coroutines.test.TestBuildersKt$runBlockingTest$deferred$1.invokeSuspend(TestBuilders.kt:50)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at kotlinx.coroutines.test.TestCoroutineDispatcher.dispatch(TestCoroutineDispatcher.kt:50)
    at kotlinx.coroutines.internal.DispatchedContinuationKt.resumeCancellableWith(DispatchedContinuation.kt:322)
    at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:30)
    at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable$default(Cancellable.kt:25)
    at kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:110)
    at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:126)
    at kotlinx.coroutines.BuildersKt__Builders_commonKt.async(Builders.common.kt:91)
    at kotlinx.coroutines.BuildersKt.async(Unknown Source)
    at kotlinx.coroutines.BuildersKt__Builders_commonKt.async$default(Builders.common.kt:82)
    at kotlinx.coroutines.BuildersKt.async$default(Unknown Source)
    at kotlinx.coroutines.test.TestBuildersKt.runBlockingTest(TestBuilders.kt:49)
    at kotlinx.coroutines.test.TestBuildersKt.runBlockingTest(TestBuilders.kt:73)
    at at **.*******.data.repository.AddressRepositoryTest$when getAddress is called, returns false(AddressRepositoryTest.kt:49)
    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:566)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:61)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
    at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
    at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.runTestClass(JUnitTestClassExecutor.java:110)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:58)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:38)
    at org.gradle.api.internal.tasks.testing.junit.AbstractJUnitTestClassProcessor.processTestClass(AbstractJUnitTestClassProcessor.java:62)
    at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:51)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
    at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
    at com.sun.proxy.$Proxy5.processTestClass(Unknown Source)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:119)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:182)
    at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:164)
    at org.gradle.internal.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:414)
    at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
    at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:48)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:56)
    at java.base/java.lang.Thread.run(Thread.java:829)

I have tried different variations e.g.

coEvery {
    service.getAddress(123, "en", null)
}.coAnswers {
    throw Exception()
}

When running the above I get a test failure with the following stack trace:

java.lang.Exception
    at **.****.******.data.repository.AddressRepositoryTest$when getAddress is called, returns false$1$2.invokeSuspend(AddressRepositoryTest.kt:53)
    at **.****.******.data.repository.AddressRepositoryTest$when getAddress is called, returns false$1$2.invoke(AddressRepositoryTest.kt)
    at io.mockk.MockKStubScope$coAnswers$1.invokeSuspend(API.kt:2112)
    at io.mockk.MockKStubScope$coAnswers$1.invoke(API.kt)
    at io.mockk.CoFunctionAnswer$answer$1.invokeSuspend(Answers.kt:33)
    at io.mockk.CoFunctionAnswer$answer$1.invoke(Answers.kt)
    at io.mockk.JvmCoroutineCall.callCoroutine(InternalPlatformDsl.kt:212)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at io.mockk.JvmCoroutineCall.callWithContinuation(InternalPlatformDsl.kt:217)
    at io.mockk.CoFunctionAnswer.answer(Answers.kt:34)
    at io.mockk.impl.stub.AnswerAnsweringOpportunity.answer(AnswerAnsweringOpportunity.kt:14)
    at io.mockk.impl.stub.MockKStub.answer(MockKStub.kt:54)
    at io.mockk.impl.recording.states.AnsweringState.call(AnsweringState.kt:16)
    at io.mockk.impl.recording.CommonCallRecorder.call(CommonCallRecorder.kt:53)
    at io.mockk.impl.stub.MockKStub.handleInvocation(MockKStub.kt:263)
    at io.mockk.impl.instantiation.JvmMockFactoryHelper$mockHandler$1.invocation(JvmMockFactoryHelper.kt:25)
    at io.mockk.proxy.jvm.advice.Interceptor.call(Interceptor.kt:20)
    at io.mockk.proxy.jvm.advice.BaseAdvice.handle(BaseAdvice.kt:42)
    at io.mockk.proxy.jvm.advice.jvm.JvmMockKProxyInterceptor.interceptNoSuper(JvmMockKProxyInterceptor.java:45)
    at **.****.******.data.api.AddressRestService$Subclass0.getAddress(Unknown Source)
    at **.****.******.data.repository.AddressRepository$getAddress$2.invokeSuspend(AddressRepository.kt:18)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at kotlinx.coroutines.test.TestCoroutineDispatcher.dispatch(TestCoroutineDispatcher.kt:50)
    at kotlinx.coroutines.test.internal.TestMainDispatcher.dispatch(MainTestDispatcher.kt:35)
    at kotlinx.coroutines.internal.DispatchedContinuationKt.resumeCancellableWith(DispatchedContinuation.kt:322)
    at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:30)
    at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable$default(Cancellable.kt:25)
    at kotlinx.coroutines.BuildersKt__Builders_commonKt.withContext(Builders.common.kt:170)
    at kotlinx.coroutines.BuildersKt.withContext(Unknown Source)
    at **.****.******.data.repository.AddressRepository.getAddress(AddressRepository.kt:17)
    at **.****.******.data.repository.AddressRepositoryTest$when getAddress is called, returns false$1.invokeSuspend(AddressRepositoryTest.kt:56)
    at **.****.******.data.repository.AddressRepositoryTest$when getAddress is called, returns false$1.invoke(AddressRepositoryTest.kt)
    at kotlinx.coroutines.test.TestBuildersKt$runBlockingTest$deferred$1.invokeSuspend(TestBuilders.kt:50)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at kotlinx.coroutines.test.TestCoroutineDispatcher.dispatch(TestCoroutineDispatcher.kt:50)
    at kotlinx.coroutines.internal.DispatchedContinuationKt.resumeCancellableWith(DispatchedContinuation.kt:322)
    at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:30)
    at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable$default(Cancellable.kt:25)
    at kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:110)
    at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:126)
    at kotlinx.coroutines.BuildersKt__Builders_commonKt.async(Builders.common.kt:91)
    at kotlinx.coroutines.BuildersKt.async(Unknown Source)
    at kotlinx.coroutines.BuildersKt__Builders_commonKt.async$default(Builders.common.kt:82)
    at kotlinx.coroutines.BuildersKt.async$default(Unknown Source)
    at kotlinx.coroutines.test.TestBuildersKt.runBlockingTest(TestBuilders.kt:49)
    at kotlinx.coroutines.test.TestBuildersKt.runBlockingTest(TestBuilders.kt:73)
    at **.****.******.data.repository.AddressRepositoryTest.when getAddress is called, returns false(AddressRepositoryTest.kt:49)
    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:566)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:61)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
    at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
    at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.runTestClass(JUnitTestClassExecutor.java:110)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:58)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:38)
    at org.gradle.api.internal.tasks.testing.junit.AbstractJUnitTestClassProcessor.processTestClass(AbstractJUnitTestClassProcessor.java:62)
    at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:51)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
    at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
    at com.sun.proxy.$Proxy5.processTestClass(Unknown Source)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:119)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:182)
    at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:164)
    at org.gradle.internal.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:414)
    at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
    at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:48)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:56)
    at java.base/java.lang.Thread.run(Thread.java:829)

I would very much appreciate if anyone could point out where I'm going wrong.. if it is possible to mock throwing an exception with coroutines. Any tips appreciated

what's the return type from getAddress? Apart from that, you are causing the test to crash because you are throwing an exception while executing the test. — gyosida, Feb 08 '22 at 23:06
@gyosida the return type is an address dto. I will have a scenario whereby my backend might return a 501 exception. So I need to test that path. Is there a way to do this with Mockk and suspend functions? — DJ-DOO, Feb 09 '22 at 09:19
Probably related to this answer https://stackoverflow.com/a/66973130/3648678 check it out — gyosida, Feb 09 '22 at 15:48

Sergio · Accepted Answer · 2022-02-09T13:18:00.460

2

You can try to use JUnit Jupiter library, it allows to test throwing Exceptions by using assertThrows method. For example if you want to test that service.getAddress() function throws some Exception under certain conditions you can test it like the following:

assertThrows<Exception> { service.getAddress(123, "en", null) }

This assertion checks whether getAddress throws Exception exception. You can replace Exception with another type you want to test.

If you want to throw an Exception you can use throws infix function:

coEvery { service.getAddress(123, "en", null) } throws NullPointerException("Error occurred")

I guess the error you get is happening due to incorrect return value. Please try to return AddressForm object instead of throwing an Exception:

coEvery { service.getAddress(any(), any(), any()) } returns AddressForm(...)

edited Feb 09 '22 at 13:18

answered Feb 09 '22 at 09:23

Sergio

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thank you for your answer. So if I want to mock that the `getAddress()` method would throw an Exception, can I do this with Junit Jupiter? – DJ-DOO Feb 09 '22 at 12:14
with my answer you can test whether `getAddress()` function throws an exception under certain conditions. Please see my updated answer regarding throwing an Exception. – Sergio Feb 09 '22 at 12:35
thanks Sergy, yes I had updated my OP above with that, however I still get the above error when calling the suspend function `val subject = repository.getAddress(123, "en", null)` afterwards so I'm not sure what's happening there – DJ-DOO Feb 09 '22 at 12:59
please see my updated answer regarding the error you get. – Sergio Feb 09 '22 at 13:18
I have done that, I have tested the happy path. Now I want to test the unhappy path by mocking an exception being thrown – DJ-DOO Feb 09 '22 at 14:05
If you are certain that under some conditions the function throws an exception, then use `assertThrows { service.getAddress(...) }` to test it. Replace `Exception` with needed type. – Sergio Feb 09 '22 at 14:07
@Sergio But the assertThrows { service.getAddress(...) } won't work with the `getAddress(...)` as it it a suspended function. @DJ-DOO how did it work with you for marking the answer as accepted? – Mohamed Wael Aug 21 '22 at 17:24

Mock throwing of Exception with Android Coroutines

1 Answers1