Test doubles (Ruby/RSpec)

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 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 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. Ruby frameworks
39. Ruby frameworks RSpec
40. Ruby frameworks RSpec Mocha
41. Ruby frameworks RSpec Mocha RR
42. Ruby frameworks RSpec Mocha RR
43. Stubbing
44. Stubbing widget = double :widget
45. Stubbing widget = double :widget allow(widget).to receive(:foo).
 with(0) { "something" }
46. Stubbing widget = double :widget allow(widget).to receive(:foo).
 with(0) { "something" } allow(widget).
 to receive(:foo) { "something else" }
47. Stubbing widget = double :widget allow(widget).to receive(:foo).
 with(0) { "something" } allow(widget).
 to receive(:foo) { "something else" } allow(widget).to receive(:bar).
 and_raise "error!"
48. Mocking
49. Mocking widget = double :widget
50. Mocking widget = double :widget expect(widget).to receive(:foo)
51. Mocking widget = double :widget expect(widget).to receive(:foo) expect(widget).to receive(:bar).
 with(0) { "something" }
52. Mocking widget = double :widget expect(widget).to receive(:foo) expect(widget).to receive(:bar).
 with(0) { "something" } // do some stuff
53. Mocking (spy style)
54. Mocking (spy style) widget = double :widget
55. Mocking (spy style) widget = double :widget allow(widget).to receive(:foo)
56. Mocking (spy style) widget = double :widget allow(widget).to receive(:foo) // do some stuff
57. Mocking (spy style) widget = double :widget allow(widget).to receive(:foo) // do some stuff expect(widget).to have_received(:foo).
 with(42, an_instance_of(String))
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).