如何模拟void方法抛出异常？

Question

我有这样的结构:

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,我需要涵盖抛出异常的场景cacheWrapper.我正在遵循的方法是为CacheWrapper类创建一个mock ,让CacheWrapper类上的方法抛出一个RuntimeException,在一个实例SomeClient和test中设置这个mock Someclient#getEntity.问题是尝试模拟putInSharedMemory方法因为是void.我已经尝试了很多方法来做到这一点,但没有一个工作.该项目依赖于PowerMock和EasyMock.

以下是我的尝试:

1. 用EasyMock.<Void>expect.这引发了编译器错误.

2. 试图存根CacheWrapper#putInSharedMemory.没有用,因为这个错误消息引发了异常:

   java.lang.AssertionError:意外的方法调用putInSharedMemory("foo",com.company.domain.Entity @ 609fc98)

3. 为项目添加了Mockito依赖项以利用PowerMockito类的功能.但这引发了一个例外,因为它没有与EasyMock集成.这是一个例外:

   java.lang.ClassCastException:org.powermock.api.easymock.internal.invocationcontrol.EasyMockMethodInvocationControl无法强制转换为org.powermock.api.mockito.internal.invocationcontrol.MockitoMethodInvocationControl

以下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;
}

我不能改变它的实现,CacheWrapper因为它来自第三方库.另外,我无法使用,EasyMock#getLastCall因为我正在进行测试SomeClient#getEntity.

我怎么能克服这个？

Answer 1

由于您的课程都不是最终的,您可以使用"纯粹的模拟",而无需使用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; 你可以放置特定的值(如果没有被它将调用的特定方法"包围" .equals()).因此,您可以针对不同的参数不同地指导存根的行为.

此外,没有任何.replay()与Mockito,这是非常好的!

最后,请注意你也可以doCallRealMethod().在那之后,这取决于你的场景......

(注意:maven上的最后一个mockito版本是1.10.17 FWIW)

Answer 2

您正在使用EasyMock还是Mockito？两者都是不同的框架。

PowerMockito是可以与这两个框架一起使用的超集（或更多补充）。PowerMockito允许您执行Mockito或EasyMock不执行的操作。

尝试使用此方法对无效方法进行存根以引发异常：

EasyMock：

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

校验：

• http://easymock.org/api/org/easymock/internal/MocksControl.html#andVoid--
• 使EasyMock模拟对象引发异常

Mockito：

 // 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");