如何在Mockito的单元测试中模拟LocalCache

Question

My base class uses java library responsible for auditing. This Library uses Builder pattern to retrieve objects from my Java Project for Auditing Operations ( Inserts into Multiple tables by creating keys on it's own. ) This Library uses com.google.common.cache to manage cache values. ie String and Value. LoadingCache<String, Long>

sample Example of how my project uses library

auditOperation = LibraryAuditBuilder.builder()
//some param
.build()
LibraryAuditingService.process(auditOperation);

My base application and Library runs on Oracle Database and my unit tests uses HSQL database. Given all necessary scripts in @Before I would want to unit test execution of my code.

@Before method

@Before
    public void setUp() throws Exception {
    MockitoAnnotations.initMocks(this);
//create db scrips and other declarations
}

I have tried 2 approach so far

1) Created LoadingCache and put sample values in it so that UnitTest can use it later in execution.

longLoadingCache.put("4028eeb0-1d2d-daba-011d-2e36e4b2110e",(long)203);
longLoadingCache.put("4028ee14-24b4-5221-0124-b47bbb1d1232",(long)102);

2) @Mock object of LoadingCache and values in it to be used later in Tests

when(longLoadingCache.get("4028eeb0-1d2d-daba-011d-2e36e4b2110e")).thenReturn((long)203);     
when(longLoadingCache.get("4028ee14-24b4-5221-0124-b47bbb1d1232")).thenReturn((long)102);

Current output with both of above approach

- com.google.common.cache.CacheLoader$InvalidCacheLoadException: CacheLoader returned null for key 4028ee14-24b4-5221-0124-b47bbb1d1232.

So my question is, How Can I Pass/Mock values of Cache so that UnitTests don't have to look for values in Library class.

Answer 1

Consider creating your own facade bean wrapping the 3rd-party library (eg AuditProcessor). When the facade is injected using @Autowire or @Inject you can easily mock it in the test code and check if your wrapping facade (read: the library) has been properly used. If you don't trust the library you could unit test the wrapping facade and all corner cases in isolated environment without HSQL. If you want even more control you could introduce an interface (eg IAuditProcessor) and create a dummy implementation which will be @Autowired in test using Spring profiles.

To summarize:

• HSQL-based test should test if the facade is called when expected and with correct arguments
• corner cases / caching should be tested separately in isolated test cases without HSQL / Spring context

Answer 2

Although answer from @Lukasz was perfectly valid but required much more effort. After spending some hours I was able to create simpler solution for this problem. Rather then @Mock ing LocalCache , I can just @Mock class(Library class) providing cache values, as they were static values we don't care how library itself retrieves it. something like following

 busAuditOperationDao = mock(BusAuditOperationDao.class);
 busAuditProcessDao = mock(BusAuditProcessDao.class);

in @Before method I can specify whatever values I want, which will be used in @test classes

when(busAuditOperationDao.getAuditOperationIdFromGuid("4028eeb0-1d2d-daba-011d-2e36e4b2110e")).thenReturn((long) 102);
when(busAuditProcessDao.getAuditProcessIdFromGuid("4028ee14-24b4-5221-0124-b47bbb1d1232")).thenReturn((long)203);