Talk given at the SunshinePHP Uncon, about unit testing, unit testing archaeology and functional programming

1. Unit Testing
+
Functional Programming
=
<3
Alvaro Videla - RabbitMQ

2. About Me
• RabbitMQ Developer Advocate
• Blog: http://videlalvaro.github.io/
• Twitter: @old_sound

3. About Me
Co-author
!
RabbitMQ in Action
http://bit.ly/rabbitmq

4. I’m not a:

5. I’m not a:
• Application Testing Guru

6. I’m not a:
• Application Testing Guru
• TDD Advocate

7. Why is it so hard to
write tests?

8. Unit Testing
The goal of unit testing is to
isolate each part of the
program and show that the
individual parts are correct
http://en.wikipedia.org/wiki/Unit_testing

9. Unit Testing
[…] unit testing by definition only tests
the functionality of the units themselves.
http://en.wikipedia.org/wiki/Unit_testing

10. Unit Testing
[…] Therefore, it will not catch
integration errors or broader systemlevel errors (such as functions performed
across multiple units, or non-functional
test areas such as performance)
http://en.wikipedia.org/wiki/Unit_testing

11. Back to 1976

12. Test procedures:
A new approach to software verification
David J. Panzl
http://dl.acm.org/citation.cfm?id=807721&dl=ACM&coll=DL&CFID=290373956&CFTOKEN=26471516

13. Test Procedures
We propose a new medium for software
verification tests. Tests described in this
medium are complete, compact and fully
self-contained
http://dl.acm.org/citation.cfm?id=807721&dl=ACM&coll=DL&CFID=290373956&CFTOKEN=26471516

14. Test Procedures
No additional materials, instructions or
knowledge about the target program are
required to apply these tests.
http://dl.acm.org/citation.cfm?id=807721&dl=ACM&coll=DL&CFID=290373956&CFTOKEN=26471516

15. Forward to 1982

16. http://www.amazon.com/Software-Testing-Techniques-2nd-Edition/dp/1850328803/

17. Unit, Unit Testing
A unit is the smallest testable piece of
software
http://www.amazon.com/Software-Testing-Techniques-2nd-Edition/dp/1850328803/

18. Forward to 1986

19. http://www.amazon.com/Abstraction-Specification-Development-Electrical-Engineering/dp/0262121123/

20. Dogma
vs.
Reality

21. A world of
Trade Offs

22. What should
we test?

23. How much
should
we test?

24. “I get paid for code that works, not for
tests, so my philosophy is to test as
little as possible to reach a given level
of confidence”
– Kent Beck
http://stackoverflow.com/questions/153234/how-deep-are-your-unit-tests/153565#153565

25. The Hidden
Secret
Of TDD

26. The Secret of TDD

27. The Secret of TDD

28. Some books by Kent Beck

29. To write good tests
first we need to learn
how to program

31. We developers are
like those users we
like to complain so
much about

32. NIH Syndrome

33. Design evolves and
matures with time

34. Good Code sits in the
small details

35. TIPS

36. Separate pure code
from impure or stateful

37. Pure Functions

38. Pure Functions
• Referential Transparency

39. Pure Functions
• Referential Transparency
• Don’t modify external state

40. Pure Functions
• Referential Transparency
• Don’t modify external state
• Don’t produce side effects

41. What’s wrong with this code?
if($player->getScore() > 0) {
$player->setSwizzle(7);
} else {
$player->setSwizzle(
$player->getSwizzle() + 1
);
}
https://dl.dropboxusercontent.com/u/7810909/docs/what-does-fp-mean/what-does-fp-mean/chunk-html/ar01s05.html

42. What’s wrong with this code?
$newScore = $player->getScore() > 0
? 7
: $player->getSwizzle() + 1;
!
$player->setSwizzle($newScore);
https://dl.dropboxusercontent.com/u/7810909/docs/what-does-fp-mean/what-does-fp-mean/chunk-html/ar01s05.html

43. Score calculation can
be moved into its
own function

44. Score calculation can
be tested now

45. First write
Pure Code

46. Add impure code step
by step when needed

47. Write
Composable
Code

48. Function Composition
http://en.wikipedia.org/wiki/Function_(mathematics)

49. Function Composition
http://en.wikipedia.org/wiki/Function_(mathematics)

50. This looks familiar

51. “Many UNIX programs do quite trivial
tasks in isolation, but, combined with
other programs, become general and
useful tools.”
http://math.albany.edu/math/pers/hammond/unixphil.html

52. Number of open connections per IP
netstat -ntu | awk '{print $5}' |
cut -d: -f1 | sort | uniq -c | sort -n
http://www.commandlinefu.com/commands/view/1767/number-of-open-connections-per-ip.

53. Why don’t we just
code in this style?

54. This seems familiar
again…

55. Welcome to
Functional
Programming

56. “Writing unit tests is reinventing
functional programming
in non-functional languages”
http://noss.github.io/2009/02/25/writing-unit-tests-is-reinventing-functional-programming-in-non-functional-languages.html

57. What can we learn from
Functional Programming?

58. The proper use of Types

59. What does ‘null’ mean?

60. What does
‘true|false’ mean?

61. Functions with just one
responsibility

62. Radical separation of pure
code from impure code

63. Let’s see an example

64. Food for Thought
http://thinking-forth.sourceforge.net

65. Food for Thought
http://www.amazon.com/Data-Reality-Perspective-Perceiving-Information/dp/1935504215/

66. “Inside every well- written
large program
is a well-written small
program”
http://www.linfo.org/q_programming.html

67. Questions?

68. Thanks!
http://twitter.com/old_sound
http://github.com/videlalvaro
http://www.slideshare.net/old_sound