如何模擬void方法拋出異常？

Question

我有這樣的結構：

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);
    }
}

我的客戶端類（你可以說它看起來像這樣）：

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;
    }
}

我正在為SomeClient#getEntity方法創建單元測試，並且必須涵蓋所有方案。 例如，我需要介紹cacheWrapper拋出異常的cacheWrapper 。 我正在遵循的方法是為CacheWrapper類創建一個模擬，使CacheWrapper類上的方法拋出RuntimeException ，在SomeClient的實例中設置這個mock並測試Someclient#getEntity 。 問題是在嘗試模擬putInSharedMemory方法時因為void 。 我已經嘗試了很多方法來做到這一點，但沒有一個工作。 該項目依賴於PowerMock和EasyMock 。

以下是我的嘗試：

1. 使用EasyMock.<Void>expect 。 這引發了編譯器錯誤。

2. 試圖存根CacheWrapper#putInSharedMemory 。 沒有用，因為這個錯誤消息引發了異常：

   java.lang.AssertionError：意外的方法調用putInSharedMemory（“foo”，com.company.domain.Entity @ 609fc98）

3. 為項目添加了Mockito依賴項以利用PowerMockito類的功能。 但這引發了一個例外，因為它沒有與EasyMock集成。 這是一個例外：

   java.lang.ClassCastException：org.powermock.api.easymock.internal.invocationcontrol.EasyMockMethodInvocationControl無法強制轉換為org.powermock.api.mockito.internal.invocationcontrol.MockitoMethodInvocationControl

以下是此單元測試示例的代碼：

@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;
}

我無法更改CacheWrapper的實現，因為它來自第三方庫。 另外，我不能使用EasyMock#getLastCall因為我正在對SomeClient#getEntity進行測試。

我怎么能克服這個？

Answer 1

由於您的課程都不是最終的，您可以使用“純粹的模擬”，而無需使用PowerMockito：

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

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

請注意，存根的“方法參數”實際上是參數匹配器; 你可以放置特定的值（如果沒有被特定方法“包圍”，它將調用.equals() ）。 因此，您可以針對不同的參數不同地指導存根的行為。

此外，不需要任何與Mockito的.replay() ，這是非常好的！

最后，請注意您也可以執行doCallRealMethod() 。 在那之后，這取決於你的場景......

（注意：maven上的最后一個mockito版本是1.10.17 FWIW）

Answer 2

你在使用EasyMock還是Mockito？ 兩者都是不同的框架。

PowerMockito是可以與這兩個框架一起使用的超集（或更多補充）。 PowerMockito允許您執行Mockito或EasyMock不能執行的操作。

試試這個用於存根void方法來拋出異常：

EasyMock的：

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

校驗：

• http://easymock.org/api/org/easymock/internal/MocksControl.html#andVoid--
• 獲取EasyMock模擬對象以拋出異常

的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");

Answer 3

使用expectLastCall ，如：

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