This document discusses different approaches to unit testing with mocks using Mockito. It explains that mocks allow isolating dependencies to test units in isolation. It compares directly mocking dependencies with Mockito's mocking features like stubbing, argument matchers, custom argument matchers, argument capture, and verification. Mockito provides cleaner mocking by separating stubbing from verification and supporting flexible argument matching.

1. unit testing on the rocks!

2. Why mock?

3. Isolation

4. Example
AccountController
HellotxtManagement
+addAccount
+deleteAccount
...
...

5. Example
AccountController
HellotxtManagement
+addAccount
+deleteAccount
...
...

6. The no-so-good way
HellotxtManagement
...
HellotxtManagementMock
void addAccount(){
//do what I want
}
..

7. The no-so-good way
HellotxtManagement
...
HellotxtManagementMock HellotxtManagementMock2
void addAccount(){ void addAccount(){
//do what I want //now do this
} }
.. ..

8. The no-so-good way
HellotxtManagement
...
HellotxtManagementMock HellotxtManagementMock2 HellotxtManagementMock3
void addAccount(){ void addAccount(){ void addAccount(){
//do what I want //now do this //throw exception
} } }
.. .. ..

10. The mockito way

11. Test Workflow
1. Create Mock
2. Stub
3. Invoke
4. Verify
5. Assert expectations

12. Creating a Mock
import static org.mockito.Mockito.*;
...
// You can mock concrete classes, not only interfaces
LinkedList mockedList = mock(LinkedList.class);

13. Stubbing
// stubbing
when(mockedList.get(0)).thenReturn("first");
when(mockedList.get(1)).thenThrow(new RuntimeException());

14. What’s going on?
// following prints "first"
System.out.println(mockedList.get(0));
// following throws runtime exception
System.out.println(mockedList.get(1));
// following prints "null" because get(999) was not stubbed
System.out.println(mockedList.get(999));

15. Verify
// Although it is possible to verify a stubbed invocation, usually it's
// just redundant
// If your code cares what get(0) returns then something else breaks
// (often before even verify() gets executed).
// If your code doesn't care what get(0) returns then it should not be
// stubbed. Not convinced? See here.
verify(mockedList).get(0);

16. What about void
methods?
• Often void methods you just verify them.
//create my mock and inject it to my unit under test
DB mockedDb = mock(DB.class);
MyThing unitUnderTest = new MyThing(mockedDb);
//invoke what we want to test
unitUnderTest.doSothing();
//verify we didn't forget to save my stuff.
verify(mockedDb).save();

17. What about void
methods?
• Although you can also Stub them to throw
an exception.
@Test(expected = HorribleException.class)
public void test3() throws Exception {
// create my mock and inject it to my unit under test
Oracle oracleMock = mock(Oracle.class);
MyThing unitUnderTest = new MyThing(oracleMock);
String paradox = "This statement is false";
// stub
doThrow(new HorribleException()).when(oracleMock).thinkAbout(paradox);
unitUnderTest.askTheOracle(paradox);
}

18. Argument Matchers
when(hellotxtManagementMock.addAccount(Mockito.any(Session.class), Mockito.anyString(),
Mockito.anyMap(), Mockito.anyString())).thenReturn(account);

19. Custom Argument
Matcher
Mockito.when(hellotxtManagementMock.getAuthenticationInfo(Mockito.argThat(new IsValidSession()),
Mockito.eq(Networks.FACEBOOK))).thenReturn(expectedResult);
...
private class IsValidSession extends ArgumentMatcher<Session> {
@Override
public boolean matches(Object argument) {
return argument instanceof Session
&& ((Session) argument).getSessionId().equals(TestValues.VALID_SESSION_ID);
}
}

20. Argument Capture
ArgumentCaptor<Session> sessionCaptor = ArgumentCaptor.forClass(Session.class);
...
ModelAndView result = accountController.addAccount(json.toString(), sessionId, deviceType,
deviceId, networkId);
...
verify(hellotxtManagementMock).addAccount(sessionCaptor.capture(), Mockito.eq(networkId),
Mockito.eq(parameters), Mockito.eq(redirectUrl));
...
assertEquals(sessionId, sessionCaptor.getValue().getSessionId());
assertEquals(deviceType, sessionCaptor.getValue().getDevice().getType().name());
assertEquals(deviceId, sessionCaptor.getValue().getDevice().getUid());