我如何模拟一个 void 方法来抛出异常？

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);
    }
}

还有我的客户class（你可以这么说）：

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场景。例如，我需要涵盖 cacheWrapper 抛出异常的场景。我遵循的方法是为 CacheWrapper class 创建一个模拟，使 CacheWrapper class 上的方法抛出一个 RuntimeException，设置这个模拟SomeClient 的实例和测试 Someclient#getEntity。问题是在尝试模拟 putInSharedMemory 方法时因为是 void。我已经尝试了很多方法来做到这一点，但其中 none 有效。 该项目依赖于 PowerMock 和 EasyMock。

这是我的尝试：

使用EasyMock.<Void>expect。这引发了编译器错误。
试图存根 CacheWrapper#putInSharedMemory。没有工作，因为引发了异常并显示此错误消息：

java.lang.AssertionError: Unexpected method call putInSharedMemory("foo", com.company.domain.Entity@609fc98)
向项目添加了 Mockito 依赖项 以利用 PowerMockito class 的功能。但这引发了一个异常，因为它没有与 EasyMock 集成。这是引发的异常：

java.lang.ClassCastException: org.powermock.api.easymock.internal.invocationcontrol.EasyMockMethodInvocationControl cannot be cast to org.powermock.api.mockito.internal.invocationcontrol.MockitoMethodInvocationControl

这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 CacheWrapper 的实现，因为它来自第三方库。另外，我不能使用 EasyMock#getLastCall 因为我正在 SomeClient#getEntity.

上执行测试

我该如何克服这个问题？

Answer 1

使用expectLastCall，如：

    cacheWrapper.putInSharedMemory(EasyMock.anyObject(), EasyMock.anyObject())
    EasyMock.expectLastCall().andThrow(new RuntimeException("This is an intentional Exception")).anyTimes();

Answer 2

由于您的类中的 none 是最终的，您可以使用 "pure mockito" 而无需求助于 PowerMockito：

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

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

请注意，存根的 "method arguments" 实际上是参数匹配器；您可以输入特定值（如果不是通过特定方法 "surrounded"，它将调用 .equals()）。因此，您可以针对不同的参数以不同方式引导存根的行为。

此外，Mockito 不需要任何类型的 .replay()，这非常好！

最后，请注意您也可以 doCallRealMethod()。之后就看你的场景了...

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

Answer 3

您使用的是 EasyMock 还是 Mockito？两者是不同的框架。

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 允许您做 Mockito 或 EasyMock 做不到的事情。

尝试使用此方法对 void 方法进行存根以抛出异常：

EasyMock:

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

检查：

http://easymock.org/api/org/easymock/internal/MocksControl.html#andVoid--
Getting EasyMock mock objects to throw Exceptions

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");

我如何模拟一个 void 方法来抛出异常？

How can I mock a void method to throw an exception?

java

unit-testing

exception

powermock

easymock