Mockito doThrow() 方法使我的测试因给定异常而失败

Question

I'm testing the error case for when my injected StatefulBeanToCsv dependency throws an exception. However, Mockito's doThrow() method is just making my test fail, rather than allowing that exception to be verified using assertThrows() .

I'm injecting my StatefulBeanToCsv dependency through a BeanFactory rather than constructor/setter injection, because I need to pass it a Writer as an argument.

The test is below, and fails at the asterisk. The CSV bean works okay in my success tests - the main difference I can think of in this case is the use of the do / when Mockito pattern rather than the when / then one used elsewhere (which doesn't allow exceptions to be thrown from void methods):

@Test
    void willThrowSwaggerListToCsvExceptionIfCsvWriterThrowsCsvException() throws CsvFieldAssignmentException {
        // given
        List<ApiSummary.Endpoint> endpointList = getEndpointList(6);
        doReturn(endpointBeanToCsvMock)
                .when(beanFactoryMock).getBean(eq(StatefulBeanToCsv.class), eq(ApiSummary.Endpoint.class), any(Writer.class), any(String[].class));
        doThrow(CsvFieldAssignmentException.class)
*               .when(endpointBeanToCsvMock).write(endpointList);
        // when, then
        assertThrows(SwaggerToCsvException.class, () -> underTest.listToResource(endpointList, ApiSummary.Endpoint.class));
    }

The method I'm testing is below (and I'm expecting the void "write" method at the asterisk to throw the exception).

public <T> ByteArrayResource listToResource(List<T> beanList, Class<T> clazz, String... columnOrder) {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        try (Writer writer = new OutputStreamWriter(out)) {
            StatefulBeanToCsv<T> beanToCsv = beanFactory.getBean(StatefulBeanToCsv.class, clazz, writer, columnOrder);
*           beanToCsv.write(beanList);
        } catch (CsvFieldAssignmentException | IOException e) {
            throw new SwaggerToCsvException("Error converting List of type " + clazz.getSimpleName() + " to csv", e);
        }
        byte[] bytes = out.toByteArray();
        return new ByteArrayResource(bytes);
    }

Am I missing something?

Edit - stack trace:

java.lang.InstantiationError: com.opencsv.exceptions.CsvFieldAssignmentException

    at jdk.internal.reflect.GeneratedSerializationConstructorAccessor3.newInstance(Unknown Source)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
    at org.objenesis.instantiator.sun.SunReflectionFactoryInstantiator.newInstance(SunReflectionFactoryInstantiator.java:48)
    at org.objenesis.ObjenesisBase.newInstance(ObjenesisBase.java:73)
    at org.mockito.internal.creation.instance.ObjenesisInstantiator.newInstance(ObjenesisInstantiator.java:21)
    at org.mockito.internal.stubbing.answers.ThrowsExceptionForClassType.getThrowable(ThrowsExceptionForClassType.java:23)
    at org.mockito.internal.stubbing.answers.AbstractThrowsException.validateFor(AbstractThrowsException.java:43)
    at org.mockito.internal.stubbing.InvocationContainerImpl.addAnswer(InvocationContainerImpl.java:72)
    at org.mockito.internal.stubbing.InvocationContainerImpl.setMethodForStubbing(InvocationContainerImpl.java:128)
    at org.mockito.internal.handler.MockHandlerImpl.handle(MockHandlerImpl.java:53)
    at org.mockito.internal.handler.NullResultGuardian.handle(NullResultGuardian.java:29)
    at org.mockito.internal.handler.InvocationNotifierHandler.handle(InvocationNotifierHandler.java:33)
    at org.mockito.internal.creation.bytebuddy.MockMethodInterceptor.doIntercept(MockMethodInterceptor.java:82)
    at org.mockito.internal.creation.bytebuddy.MockMethodInterceptor.doIntercept(MockMethodInterceptor.java:56)
    at org.mockito.internal.creation.bytebuddy.MockMethodInterceptor$DispatcherDefaultingToRealMethod.interceptSuperCallable(MockMethodInterceptor.java:141)
    at com.opencsv.bean.StatefulBeanToCsv$MockitoMock$321003460.write(Unknown Source)
    at com.foo.myproject.csv.CsvFactoryTest.willThrowSwaggerListToCsvExceptionIfCsvWriterThrowsCsvException(CsvFactoryTest.java:96)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$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$6(TestMethodTestDescriptor.java:210)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:206)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:131)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:65)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
    at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)

Answer 1

As M.Deinum mentions in a comment, the error here isn't that the exception is being thrown, but rather that Mockito is failing to instantiate the exception, in order to throw it for you.

Note that the example in the Mockito documentation shows the exception being instantiated - that is, the doThrow() method is taking an instance of the exception, not the class of the exception that you want to throw:

doThrow(new RuntimeException()).when(mockedList).clear();

The Javadoc does also show that you can provide a class, as you have, and says that it will be instantiated, but doesn't give details on what constructors are required. Without trying it myself, I would guess that will only work for exceptions with a default (no-args) constructor.