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
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