Test doubles (Java/Mockito)

Slides from coding dojo talk at work

Transcript

1. Test doubles (stubs and mocks)
2. TDD
3. TDD
4. TDD
5. Refactoring
6. Refactoring
7. Refactoring
8. Queries & commands (a small digression)
9. Queries User
 repository Authenticator Session
10. Queries User
 repository Authenticator Session findUser("bob");
11. Queries User
 repository Authenticator Session [a User object]
12. Commands User
 repository Authenticator Session setUser(user);
13. Test doubles (stubs & mocks)
14. Stubbing a query Stub
 repository Authenticator Session findUser("bob");
15. Stubbing a query Stub
 repository Authenticator Session [a User object]
16. A stub simply returns canned values
17. A stub simply returns canned values ! (which may be real value objects or other test doubles)
18. Mocking a command User
 repository Authenticator Mock
 Session setUser(user);
19. A mock verifies methods were called
20. Stub queries Mock commands
21. Outside-in design
22. Identify responsibilities
23. Identify responsibilities Does the class have a single responsibility?
24. Identify responsibilities Does the class have a single responsibility? Yes test drive behaviour as normal
25. Identify responsibilities Does the class have a single responsibility? Yes test drive behaviour as normal No identify collaborating roles (interfaces) specify interactions using test doubles
26. Implement collaborators
27. Implement collaborators For each role identified at the layer above…
28. Implement collaborators For each role identified at the layer above… Identify responsibilities Does the class have a single responsibility? Yes test drive behaviour as normal No identify collaborating roles (interfaces) specify interactions using test doubles
29. Rules*
30. Rules* A class can arrange collaborators or do work
31. Rules* A class can arrange collaborators or do work Stub queries; mock commands
32. Rules* A class can arrange collaborators or do work Stub queries; mock commands Doubles can return value objects or other doubles (but not objects with behaviour)
33. Rules* A class can arrange collaborators or do work Stub queries; mock commands Doubles can return value objects or other doubles (but not objects with behaviour) Don’t stub or mock value objects or primitives
34. Rules* A class can arrange collaborators or do work Stub queries; mock commands Doubles can return value objects or other doubles (but not objects with behaviour) Don’t stub or mock value objects or primitives Don’t stub or mock the object under test
35. Rules* A class can arrange collaborators or do work Stub queries; mock commands Doubles can return value objects or other doubles (but not objects with behaviour) Don’t stub or mock value objects or primitives Don’t stub or mock the object under test
36. Rules* A class can arrange collaborators or do work Stub queries; mock commands Doubles can return value objects or other doubles (but not objects with behaviour) Don’t stub or mock value objects or primitives Don’t stub or mock the object under test *more what you’d call ‘guidelines’ than actual rules
37. Show me the code!
38. Java frameworks
39. Java frameworks EasyMock
40. Java frameworks EasyMock JMock
41. Java frameworks EasyMock JMock Mockito
42. Java frameworks EasyMock JMock Mockito JMockit
43. Java frameworks EasyMock JMock Mockito JMockit PowerMock
44. Java frameworks EasyMock JMock Mockito JMockit PowerMock
45. Stubbing
46. Stubbing import static org.mockito.Mockito.*;
47. Stubbing import static org.mockito.Mockito.*; Widget widget = mock(Widget.class);
48. Stubbing import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); when(widget.foo(0)).
 thenReturn("something");
49. Stubbing import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); when(widget.foo(0)).
 thenReturn("something"); when(widget.foo(anyInt())).
 thenReturn("something else");
50. Stubbing import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); when(widget.foo(0)).
 thenReturn("something"); when(widget.foo(anyInt())).
 thenReturn("something else"); when(widget.bar(any())).
 thenThrow(new RuntimeException());
51. Mocking
52. Mocking import static org.mockito.Mockito.*;
53. Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class);
54. Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); // do some stuff
55. Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); // do some stuff verify(widget).foo(1);
56. Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); // do some stuff verify(widget).foo(1); verify(widget).bar();
57. Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); // do some stuff verify(widget).foo(1); verify(widget).bar(); verify(widget).baz(42, isA(Quuz.class));
58. Exercise Use doubles to test-drive a Transaction class with a transfer method that takes an amount and two Account objects (source and destination). When transfer is called, the source account should receive debit(amount) and the destination account credit(amount).