Mocking Reflection based calls

Question

I am trying to mock some reflection based methods. Below you can see the details,

Class Under Test

public class TracerLog {
    @AroundInvoke
    public Object logCall(InvocationContext context) throws Exception {
        Logger logger = new Logger();
        String message = "INFO: Invoking method - " 
                + context.getMethod().getName() + "() of Class - " 
                + context.getMethod().getDeclaringClass();

        logger.write(message);
        return context.proceed();
    }
}

Test

public class TracerLogTest {

@Mock
InvocationContext mockContext;
@Mock
Logger mockLogger;
@InjectMocks
private TracerLog cut = new TracerLog();

@BeforeMethod
public void setup() {
    MockitoAnnotations.initMocks(this);
}

@Test
public void logCallTest() throws Exception {
    when(mockContext.proceed()).thenReturn(true);
    when(mockContext.getMethod().getDeclaringClass().getName()).thenReturn("someClass");
    cut.logCall(mockContext);
    verify(mockContext).proceed();
}

}

or

@Test
public void logCallTest() throws Exception {
    when(mockContext.proceed()).thenReturn(true);
    when(mockContext.getMethod().getName()).thenReturn("someMethod");
    when(mockContext.getMethod().getDeclaringClass().getName()).thenReturn("someClass");
    cut.logCall(mockContext);
    verify(mockLogger).write(anyString());
    verify(mockContext).proceed();
}

But, the tests fail with a NullPointerException. I understand that I am doing something wrong against mocking concepts, but I do not understand what it is. Could you please throw some light on it and also suggest me how this method can be tested?

Thanks.

Answer 1

You need a Method object and a Class object. As per your comment, Mockito cannot mock a Method, so you'll need a real one. I haven't tested this, but I believe this would work. Instead of:

when(mockContext.getMethod().getName()).thenReturn("someMethod");
when(mockContext.getMethod().getDeclaringClass().getName()).thenReturn("someClass");

You need:

// any method will do, but here is an example of how to get one.
Method testMethod = this.getClass().getMethod("logCallTest");

when(mockContext.getMethod()).thenReturn(testMethod);

Obviously, getName() will not return "someMethod" anymore and getDeclaringClass().getName() will return the name of this test class (in the example), but although you couldn't pick what they return, what they return is still deterministic, so you should be able to verify anything you need. (Of course, if you needed to spy or verify that a call was made on the Method object itself, you're still stuck.)

Answer 2

Yeah the problem is that mockContext.getMethod() is going to return null. So every time you run this, then call something on the result (getDeclaringClass() or getName()) you'll get the NPE. You probably want to use the RETURNS_DEEP_STUBS default answer, when you set up the mock. Something like

@Mock( answer = RETURNS_DEEP_STUBS ) private InvocationContext mockContext; 

should do the trick.