1. Mock Objects in Action
Paulo Caroli & Sudhindra Rao
Agile 2009
© ThoughtWorks 2008

2. About us

3. About us
Paulo Caroli
&
Sudhindra Rao

4. About us
Hands-on developers

5. About us
Open Source

6. About us
ThoughtWorks

7. About us
TDD enthusiasts

8. Agenda

9. Agenda
• History
• Design for Testability
• Dependent Components
• Mock Objects in Action
• Top Offenders
• Q&A

10. History

11. Once upon a time we started writing
Unit Tests…

12. Then we started using unit tests
frameworks…

13. And soon after we started creating (and
re-creating) data and implementations
to help drive our tests…

14. Then we came across Mock Objects
frameworks…

15. But frameworks don’t work by
themselves!

17. public class Greeting {
private Translator translator;
private final String HELLO = "Hello";
public Greeting() {
this.translator = new TranslatorImpl();
}
public String sayHello(String language, String name) {
String message = HELLO;
// no need to call translator if the language is English
if (!language.equals("English")){
message = translator.translate("English", language, HELLO );
}
return message + " " + name;
}
}

18. Design for Testability

20. © ThoughtWorks 2008
public class Greeting {
private Translator translator;
private final String HELLO = "Hello";
public Greeting(Translator translator) {
this.translator = translator;
}
public String sayHello(String language, String name) {
String message = HELLO;
// no need to call translator if the language is English
if (!language.equals("English")){
message = translator.translate("English", language, HELLO );
}
return message + " " + name;
}
}

21. Mock Objects
Mock Objects enable
your unit test to mimic behavior and
verify expectations on dependent
components.

23. import static org.mockito.Mockito.*;
public class GreetingTest{
@Test
public void shouldGreetInSomeLanguage(){
// setup
Translator translator = mock(Translator.class);
Greeting greeting = new Greeting(translator);
when(translator.translate("English", "French”,"Hello")).
thenReturn("Bonjour");
// execute
assertEquals("Bonjour Madame",
greeting.sayHello("French", "Madame"));
// verify
verify(translator).translate("English", "French", "Hello");
}
}

24. Mock Objects
Mock Objects enable
your unit test to mimic behavior and
verify expectations on dependent
components.

25. Mock Objects
Mock Objects enable
your unit test to mimic behavior and
verify expectations on dependent
components.

26. Dependent Components

27. Component
Component
© ThoughtWorks 2008
A
A
Component
Component
B
B
Dependent
Components

28. Object Graphs

29. Third Party

30. Very Slow

31. Remote
Component

32. Database
Component

33. Circular
Dependency

34. Complex
Set-up

35. Exceptional
Behavior

36. Time Dependent
Behavior

37. My co-worker's
component

38. Mock Objects In Action

39. © ThoughtWorks 2008

40. Mock Objects
in Action

41. Mock Objects
in Action

42. Code Watch

43. Mock Objects
Top Offenders

44. Test readability

45. Replacement for
integration test

46. Unnecessary
Mock (ex:
simple Value
Object)

47. Mock context confusion

48. Mock return a Mock

49. Abuse of mocks
(instead: FakeDB, Dummy data, Stub,
Test Fixture)

50. Blaming the framework

51. Mock Objects in Action
Thanks for attending!
Questions?
Paulo Caroli & Sudhindra Rao
pcaroli@thoughtworks.com
srao@thoughtworks.com

52. Recommended links
http://xunitpatterns.com/Mock%20Object.html
http://developer-in-test.blogspot.com/
http://misko.hevery.com/code-reviewers-guide/
http://codebetter.com/blogs/jeremy.miller/archive/2006/01/10/136407.aspx
http://martinfowler.com/articles/mocksArentStubs.html
http://www.jmock.org/oopsla2004.pdf
http://mocksamples.com/