如何模拟 void 方法来引发异常？

unit-testing exception java powermock easymock

2022-09-03 05:35:24

我有一个这样的结构：

public class CacheWrapper {
    private Map<Object, Object> innerMap;

    public CacheWrapper() {
        //initialize the innerMap with an instance for an in-memory cache
        //that works on external server
        //current implementation is not relevant for the problem
        innerMap = ...;
    }

    public void putInSharedMemory(Object key, Object value) {
        innerMap.put(key, value);
    }

    public Object getFromSharedMemory(Object key) {
        return innerMap.get(key);
    }
}

我的客户端类（你可以说它看起来像这样）：

public class SomeClient {
    //Logger here, for exception handling
    Logger log = ...;
    private CacheWrapper cacheWrapper;
    //getter and setter for cacheWrapper...

    public Entity getEntity(String param) {
        Entity someEntity = null;
        try {
            try {
                entity = cacheWrapper.getFromSharedMemory(param);
            } catch (Exception e) {
                //probably connection failure occurred here
                log.warn("There was a problem when getting from in-memory " + param + " key.", e);
            }
            if (entity == null) {
                entity = ...; //retrieve it from database
                //store in in-memory cache
                try {
                    cacheWrapper.put(param, entity);
                } catch (Exception e) {
                    //probably connection failure occurred here
                    log.warn("There was a problem when putting in in-memory " + param + " key.", e);
                }
            }
        } catch (Exception e) {
            logger.error(".......", e);
        }
        return entity;
    }
}

我正在为SomeClient#getEntity方法创建单元测试，并且必须涵盖所有方案。例如，我需要介绍由抛出异常的情况。我遵循的方法是为类创建一个模拟，使类上的方法抛出一个，在的实例中设置这个模拟并进行测试。问题是当试图模拟方法时，因为是。我已经尝试了很多方法来做到这一点，但没有一个有效。该项目具有PowerMock和EasyMock的依赖项。cacheWrapperCacheWrapperCacheWrapperRuntimeExceptionSomeClientSomeclient#getEntityputInSharedMemoryvoid

以下是我的尝试：

用。这引发了编译器错误。EasyMock.<Void>expect
已尝试存根。不起作用，因为引发了异常，并显示以下错误消息：CacheWrapper#putInSharedMemory

java.lang.AssertionError： Unexpected method call putInSharedMemory（“foo”， com.company.domain.Entity@609fc98）
将 Mockito 依赖项添加到项目中，以利用类的功能。但这引发了一个例外，因为它没有与EasyMock集成。这是引发的异常：PowerMockito

java.lang.ClassCastException： org.powermock.api.easymock.internal.invocationcontrol.EasyMockMethodInvocationControl 不能 cast to org.powermock.api.mockito.internal.invocationcontrol.MockitoMethodInvocationControl

下面是此单元测试示例的代码：

@Test
public void getEntityWithCacheWrapperException() {
    CacheWrapper cacheWrapper = mockThrowsException();
    SomeClient someClient = new SomeClient();
    someClient.setCacheWrapper(cacheWrapper);
    Entity entity = someClient.getEntity();
    //here.....................^
    //cacheWrapper.putInSharedMemory should throw an exception

    //start asserting here...
}

//...

public CacheWrapper mockThrowsException() {
    CacheWrapper cacheWrapper = PowerMock.createMock(CacheWrapper.class);
    //mocking getFromSharedMemory method
    //this works like a charm
    EasyMock.expect(cacheWrapper.getFromSharedMemory(EasyMock.anyObject()))
        .andThrow(new RuntimeException("This is an intentional Exception")).anyTimes();

    //mocking putInSharedMemory method
    //the pieces of code here were not executed at the same time
    //instead they were commented and choose one approach after another

    //attempt 1: compiler exception: <Void> is not applicable for <void>
    EasyMock.<Void>expect(cacheWrapper.putInSharedMemory(EasyMock.anyObject(), EasyMock.anyObject()))
        .andThrow(new RuntimeException("This is an intentional Exception")).anyTimes();

    //attempt 2: stubbing the method
    //exception when executing the test:
     //Unexpected method call putInSharedMemory("foo", com.company.domain.Entity@609fc98)
    Method method = PowerMock.method(CacheWrapper.class, "putInSharedMemory", Object.class, Object.class);
    PowerMock.stub(method).toThrow(new RuntimeException("Exception on purpose."));

    //attempt 3: added dependency to Mockito integrated to PowerMock
    //bad idea: the mock created by PowerMock.createMock() belongs to EasyMock, not to Mockito
    //so it breaks when performing the when method
    //exception:
    //java.lang.ClassCastException: org.powermock.api.easymock.internal.invocationcontrol.EasyMockMethodInvocationControl
    //cannot be cast to org.powermock.api.mockito.internal.invocationcontrol.MockitoMethodInvocationControl
    //at org.powermock.api.mockito.internal.expectation.PowerMockitoStubberImpl.when(PowerMockitoStubberImpl.java:54)
    PowerMockito.doThrow(new RuntimeException("Exception on purpose."))
        .when(cacheWrapper).putInSharedMemory(EasyMock.anyObject(), EasyMock.anyObject());

    PowerMock.replay(cacheWrapper);
    return cacheWrapper;
}

我无法更改的实现，因为它来自第三方库。另外，我无法使用，因为我正在执行测试。CacheWrapperEasyMock#getLastCallSomeClient#getEntity

我该如何克服这个问题？

答案 1

由于您的任何类都不是最终的，因此您可以使用“纯嘲笑”而不诉诸PowerMockito：

final CacheWrapper wrapper = Mockito.spy(new CacheWrapper());

Mockito.doThrow(something)
    .when(wrapper).putInSharedMemory(Matchers.any(), Matchers.any());

请注意，存根的“方法参数”实际上是参数匹配器;您可以放置特定值（如果没有被特定方法“包围”，它将调用）。因此，您可以针对不同的参数以不同的方式指导存根的行为。.equals()

另外，不需要任何与Mockito在一起，这非常好！.replay()

最后，请注意，您也可以。之后，这取决于您的方案...doCallRealMethod()

（注意：maven 上可用的最后一个 mockito 版本是 1.10.17 FWIW）

答案 2

您使用的是EasyMock还是Mockito？两者都是不同的框架。

PowerMockito是一个超集（或更多的补充），可以与这两个框架一起使用。PowerMockito允许你做Mockito或EasyMock没有做的事情。

尝试这样做，以存根 void 方法引发异常：

易上手：

// First make the actual call to the void method.
cacheWrapper.putInSharedMemory("key", "value");
EasyMock.expectLastCall().andThrow(new RuntimeException());

检查：

莫基托：

 // Create a CacheWrapper spy and stub its method to throw an exception.
 // Syntax for stubbing a spy's method is different from stubbing a mock's method (check Mockito's docs).
 CacheWrapper spyCw = spy(new CacheWrapper()); 
 Mockito.doThrow(new RuntimeException())
     .when(spyCw)
     .putInSharedMemory(Matchers.any(), Matchers.any());

 SomeClient sc = new SomeClient();
 sc.setCacheWrapper(spyCw);

 // This will call spyCw#putInSharedMemory that will throw an exception.
 sc.getEntity("key");