Mastering Mock Objects: Enhancing Unit Testing with Paulo Caroli and Sudhindra Rao

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. publicclass Greeting { private Translator translator; privatefinalString 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. publicclass Greeting { private Translator translator; privatefinalString 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; } } © ThoughtWorks 2008

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

23.                   import static org.mockito.Mockito.*; publicclass GreetingTest{                         @Test publicvoid 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. Dependent Components Component A Component B © ThoughtWorks 2008

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