Why should you test, how should you start, what about legacy system? Why are tests the most important part of your code? Whats wrong with UI tests?

1. Unit testing on Android:
why and how?
DevFest Bucharest
Danny Preussler
@PreusslerBerlin

2. Untested Code is the Dark Matter of Software
'El Gordo' Galaxy Cluster Even Bigger Than Thought (NASA, Chandra, 04/03/14) by NASA's Marshall Space Flight Center, CC by 2.0; flickr.com/photos/nasamarshall/13901530984

3. it makes up to 90%
of the software universe
Untested Code is the Dark Matter of Software
'El Gordo' Galaxy Cluster Even Bigger Than Thought (NASA, Chandra, 04/03/14) by NASA's Marshall Space Flight Center, CC by 2.0; flickr.com/photos/nasamarshall/13901530984

4. How do we test
our apps today?

5. http://martinfowler.com/bliki/TestPyramid.html

6. Manual
UI
Service
Unit
Champ!® Mini Swirls Birthday Party Ice Cream Cones by Blue Bunny®, CC by 2.0; www.flickr.com/photos/bluebunnyicecream/5449137794

7. http://martinfowler.com/bliki/TestPyramid.html

8. The problem of
functional tests

9. Something is broken!
@PreusslerBerlin

10. What is broken?
@PreusslerBerlin

11. Where it’s broken?
@PreusslerBerlin

12. It’s end to end by definition!
@PreusslerBerlin

13. Production failures
https://www.usenix.org/system/files/conference/osdi14/osdi14-paper-yuan.pdf

14. 77% of the failures
could be reproduced
by a unit test
@PreusslerBerlin

15. 74% of the failures
are deterministic
@PreusslerBerlin

16. 58% of the catastrophic failures
where error handling
@PreusslerBerlin

17. st by PROTerry Johnston, CC by 2.0; flickr.com/photos/powerbooktrance/466709245

18. Fear by PRObrx0; CC by 2.0; flickr.com/photos/atul666/5429073525

19. Documentation!
mutually by Bruce Denis; CC by 2.0; flickr.com/photos/f2point8/5896153192

20. Unit tests
slow me down!?

21. Unit tests
slow me down!?

22. Feature development
will slow down
long term
@PreusslerBerlin

23. Customers will loose trust
@PreusslerBerlin

24. Code written in rush
will be thrown away
@PreusslerBerlin

25. The next developer
will throw it away
@PreusslerBerlin

26. The value that separates amateurs from
professionals is that velocity is a direct function
of quality.

27. The value that separates amateurs from professionals is
that velocity is a direct function of quality.
Novices believe .. that hacking is fast.

28. The value that separates amateurs from professionals is
that velocity is a direct function of quality.
Novices believe .. that hacking is fast.
The higher the quality, the faster you go.

29. The value that separates amateurs from professionals is
that velocity is a direct function of quality.
Novices believe .. that hacking is fast.
The higher the quality, the faster you go.
Every time you trade quality for speed, you slow
down. Every time.
- Uncle Bob

30. YOU are the expert!
@PreusslerBerlin

31. Don’t let someone
tell YOU how to code!
@PreusslerBerlin

32. The only way to go fast
is to go well
@PreusslerBerlin

33. @PreusslerBerlin

34. Be professional!
@PreusslerBerlin

35. YOU are not paid
to write legacy code
@PreusslerBerlin

36. Don’t ship crap!
@PreusslerBerlin

37. Your test code
is more important
than production code
@PreusslerBerlin

38. But how do we start?

39. Write testable code
@PreusslerBerlin

40. Inversion of Control
@PreusslerBerlin

41. void doSomething() {
new Something().doWhatISay();
}
Not testable!

42. void doSomething(Something something) {
something.doWhatISay();
}

43. class MyClass {
@Inject Something something;
void doSomething() {
something.doWhatISay();
}
} Dependency
Injection

44. Single responsibilities

45. Clean Code
@PreusslerBerlin

46. Respect Law of Demeter
http://enterprisecraftsmanship.com/2016/09/29/law-of-demeter-and-immutability/ @PreusslerBerlin

47. Avoid static
@PreusslerBerlin

48. Avoid singletons
@PreusslerBerlin

49. Wrap all the things
@PreusslerBerlin

50. But what about
Legacy Code?

52. New features
must have tests!
@PreusslerBerlin

53. Investigate bugs with
exploratory tests
@PreusslerBerlin

54. Explore code with
characterization tests
@PreusslerBerlinhttps://michaelfeathers.silvrback.com/characterization-testing

55. Tests will change
your architecture
step by step
@PreusslerBerlin

56. Untestable code
is bad code!
@PreusslerBerlin

57. If you
see crap,
replace it!
@PreusslerBerlin

58. Add testing in feature planning
@PreusslerBerlin

59. Strict Definition of Done
@PreusslerBerlin

60. YOU should sign
the manifesto!
@PreusslerBerlin
manifesto.softwarecraftsmanship.org

61. Test Driven Development
@PreusslerBerlin

62. TDD is fun
@PreusslerBerlin

63. Pair programming is fun
@PreusslerBerlin
Ever tried the “evil coder”?

64. Testing is fun
@PreusslerBerlin
Playground for languages and libraries

65. Don‘t ship crap!
@PreusslerBerlin

66. Thank you!
@PreusslerBerlin
We are hiring!
careers.gsa@vimn.com