Property-based Testing is a Mindset

Transcript

1. I S A M I N D S E T

   P R O P E R T Y - B A S E D T E S T I N G

2. @whatyouhide

3. None

4. Elixir

5. T E S T I N G

6. why do we test? no tests yes tests

7. unit tests

8. test "sorting" do assert sort([]) == [] assert sort([1, 2,

   3]) == [1, 2, 3] assert sort([2, 1, 3]) == [1, 2, 3] end example-based

9. table-based Input Output [] [] [1, 2, 3] [1, 2,

   3] [2, 1, 3] [1, 2, 3]

10. unit tests , but also

11. P R O P E R T I E S

12. hard to write , but...

13. valid inputs properties of output testing framework

14. github.com/whatyouhide/stream_data

15. example time: sorting lists

16. test "sorting" do assert sort([]) == [] assert sort([1, 2,

    3]) == [1, 2, 3] assert sort([2, 1, 3]) == [1, 2, 3] end

17. lists of integers

18. it's a list has the same elements it's ordered

19. check all list <- list_of(int()) do sorted = sort(list) assert

    is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

20. check all list <- list_of(int()) do sorted = sort(list) assert

    is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

21. check all list <- list_of(int()) do sorted = sort(list) assert

    is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

22. check all list <- list_of(int()) do sorted = sort(list) assert

    is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

23. check all list <- list_of(int()) do sorted = sort(list) assert

    is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

24. def sort(list), do: list

25. [32, 2, 44, -12] [1, 0] *shrinking

26. P A T T E R N S

27. circular code

28. decode(encode(term)) == term

29. property "encoding->decoding is circular" do check all bin <- binary()

    do encoded = Huffman.encode(bin) assert is_binary(encoded) assert Huffman.decode(encoded) == bin end end Huffman encoding

30. oracle model

31. my_code() == oracle_code()

32. older system less performant implementation

33. property "gives same results as Erlang impl" do check all

    bin <- binary() do assert Huffman.encode(bin) == :huffman.encode(bin) end end

34. smoke tests https://www.youtube.com/watch?v=jvwfDdgg93E

35. API: 200, 201, 400, 404 https://www.youtube.com/watch?v=jvwfDdgg93E

36. https://www.youtube.com/watch?v=jvwfDdgg93E property "only expected codes are returned" do check all

    request <- request() do response = HTTP.perform(request) assert response.status in [200, 201, 400, 404] end end

37. locally , CI

38. if System.get_env("CI") == "true" do config :stream_data, max_runs: 500 else

    config :stream_data, max_runs: 25 end

39. unit + properties

40. R E A L - W O R L D

    E X A M P L E

41. Redis parser

42. continuation parser parse(bytes) {:ok, command} {:more, function}

43. property "splitting commands at random" do check all cmd <-

    command(), split_cmd <- random_splits(cmd) do assert {:ok, _, ""} = parse_many(split_cmd) end end

44. property "splitting commands at random" do check all cmd <-

    command(), split_cmd <- random_splits(cmd) do assert {:ok, _, ""} = parse_many(split_cmd) end end

45. property "splitting commands at random" do check all cmd <-

    command(), split_cmd <- random_splits(cmd) do assert {:ok, _, ""} = parse_many(split_cmd) end end

46. S T A T E F U L T E

    S T I N G

47. model valid commands +

48. model: state + state transformations

49. commands: calls + preconditions

50. bounded-size queue

51. Max size model system

52. •push(queue, value) •resize(queue, max_size) commands

53. def push(model, _value), do: model def resize(_model, max_size), do: max_size

54. push(queue, {:some, "value"}) push(queue, [123, 3.2]) resize(queue, 1) push(queue, %{})

55. assert size(queue) <= model

56. LevelDB

57. 17 (seventeen) calls 33 (thirty three) calls

58. C O N C L U S I O N

59. find obscure bugs reduce to minimal failing input find specification

    errors keep increasing input space

60. v1.7

61. use stream_data

62. use property-based testing

63. @whatyouhide github.com/whatyouhide/stream_data