Java 如何模拟 void 方法以引发异常？

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

提问by Luiggi Mendoza

I have a structure like this:

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);
    }
}

And my client class (you could say it looks like this):

还有我的客户端类（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;
    }
}

I'm creating unit tests for SomeClient#getEntitymethodand have to cover all scenarios. For instance, I need to cover the scenario where there are exceptions thrown by cacheWrapper. The approach I'm following is to create a mock for CacheWrapperclass, make the methods on CacheWrapperclass to throw a RuntimeException, set this mock in an instance of SomeClientand test Someclient#getEntity. The problem is when trying to mock putInSharedMemorymethod because is void. I have tried lot of ways to do this but none of them work. The project has dependencies for PowerMock and EasyMock.

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. 我遵循的方法是为CacheWrapper类创建一个模拟，使CacheWrapper类上的方法抛出 a RuntimeException，在SomeClient和 test的实例中设置这个模拟Someclient#getEntity。问题是在尝试模拟putInSharedMemory方法时，因为 is void。我尝试了很多方法来做到这一点，但都没有奏效。该项目依赖于 PowerMock 和 EasyMock。

Here are my attempts:

这是我的尝试：

1. Using EasyMock.<Void>expect. This raised a compiler error.

2. Tried to stub CacheWrapper#putInSharedMemory. Didn't worked because raised an exception with this error message:

   java.lang.AssertionError: Unexpected method call putInSharedMemory("foo", com.company.domain.Entity@609fc98)

3. Added Mockito dependency to the projectto make use of the functionality of PowerMockitoclass. But this raised an exception because it doesn't integrate with EasyMock. This is the exception raised:

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

1. 使用EasyMock.<Void>expect. 这引发了编译器错误。

2. 试图存根CacheWrapper#putInSharedMemory。没有工作，因为引发了此错误消息的异常：

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

3. 向项目添加了 Mockito 依赖项以利用PowerMockito类的功能。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 无法转换为 org.powermock.api.mockito.internal.invocationcontrol.MockitoMethodInvocationControl

Here's the code for this unit test sample:

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;
}

I cannot change the implementation of CacheWrapperbecause it comes from a third party library. Also, I cannot use EasyMock#getLastCallbecause I'm performing the test on SomeClient#getEntity.

我无法更改 的实现，CacheWrapper因为它来自第三方库。此外，我无法使用，EasyMock#getLastCall因为我正在对SomeClient#getEntity.

How can I overcome this?

我怎样才能克服这个问题？

采纳答案by fge

Since none of your classes are final, you can use "pure mockito" without resorting to PowerMockito:

由于您的课程都不是最终课程，因此您可以使用“纯模拟”而无需求助于 PowerMockito：

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

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

Note that "method arguments" to a stub are in fact argument matchers; you can put specific values (if not "surrounded" by a specific method it will make a call to .equals()). So, you can guide the stub's behavior differently for different arguments.

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.equals()）。因此，您可以针对不同的参数以不同的方式引导存根的行为。

Also, no need for any kind of .replay()with Mockito, which is very nice!

此外，不需要任何类型的.replay()Mockito，这非常好！

Finally, be aware that you can doCallRealMethod()as well. After that, it depends on your scenarios...

最后，请注意，您也可以doCallRealMethod()。之后，这取决于你的场景......

(note: last mockito version available on maven is 1.10.17 FWIW)

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

回答by NiematojakTomasz

Use expectLastCall, like:

使用expectLastCall，例如：

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

回答by nhylated

Are you using EasyMock or Mockito? Both are different frameworks.

您使用的是 EasyMock 还是 Mockito？两者都是不同的框架。

PowerMockito is a superset (or more of a supplement) that can be used with both these frameworks. PowerMockito allows you to do things that Mockito or EasyMock don't.

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 不做的事情。

Try this for stubbing void methods to throw exceptions:

试试这个来存根 void 方法来抛出异常：

EasyMock:

EasyMock：

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

Check:

查看：

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

• http://easymock.org/api/org/easymock/internal/MocksControl.html#andVoid--
• 让 EasyMock 模拟对象抛出异常

Mockito:

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");